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    01 December 2020, Volume 41 Issue 6 Previous Issue    Next Issue
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    OIL AND GAS EXPLORATION
    Achievements and Potential of Petroleum Exploration in Tuha Oil and Gas Province
    LIANG Shijun
    2020, 41 (6):  631-641.  doi: 10.7657/XJPG20200601
    Abstract ( 918 )   HTML ( 1958 )   PDF (932KB) ( 584 )   Save

    Petroleum exploration in the Tuha oil and gas province started in the 1950s, but large-scale oil and gas exploration began in 1980s. Abundant exploration results have been successively achieved in Tuha basin, Santanghu basin, Yin’e basin, etc., and major breakthroughs have been made in the exploration for Jurassic coal-measure oil and gas, Permian-Triassic ultra-deep heavy oil, Paleozoic volcanic oil and gas, and tight oil and gas in Santanghu basin. Some oil-rich sags such as the Taibei sag of Tuha basin and the Malang sag of Santanghu basin have been identified with proved oil and gas reserves (equivalent) of 8.20×108 tons, indicating good economic and social benefits. Over more than 30 years of exploration, the geological understandings of coal-derived hydrocarbons, ultra-deep heavy oil reservoirs, volcanic oil reservoirs, low-pressure oil reservoirs, and tight oil and gas reservoirs have been continuously deepened, the geological theory of oil and gas accumulation and the controlling factors of oil and gas reservoirs have been clarified, and key technologies have been formed for different types of oil and gas reservoirs. The study shows that all the basins in the Tuha oil and gas province are in the stage of medium-low exploration degree, and the remaining exploration potential is large. To keep stable production, next measures should focus on: 1)fine oil and gas exploration in coal-measures, expanding exploration to the Permian and Triassic series, and deepening the exploration in the northern piedmont areas; 2)evaluating the sweet spot intervals and zones in unconventional oil reservoirs, and exploring the Paleozoic oil and gas reservoirs while finely exploring clastic oil reservoirs around Santanghu basin; and 3)taking the Tiancao sag, Chagan sag and other sags in Yin’e basin as the key exploration targets, and confirming favorable exploration blocks.

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    Paleo-Geomorphology and Its Controls on Sedimentation of the Permian Wutonggou
    CHEN Xuan, WU Chao, WANG Bo, YANG Shaochun, WANG Ya, WANG Yongchao
    2020, 41 (6):  642-650.  doi: 10.7657/XJPG20200602
    Abstract ( 403 )   HTML ( 12 )   PDF (4517KB) ( 316 )   Save

    For a long time, researchers have divergent views on the sedimentary system of the Permian Wutonggou formation in the Taibei sag, Tuha basin, and the key issue lies in the failure to accurately determine the paleo-geomorphology. In this paper, based on the moldic method and high-resolution sequence stratigraphy, the conversion interfaces of the base level cycle are determined, and the residual stratum thickness and paleo-water depth correction under the interfaces is used to recover the paleo-geomorphology of the Permian Wutonggou formation in the Taibei sag. The study results show that the dark gray mudstones developed at the first member of the Wutonggou formation can serve as the maximum lake flooding surface and the upper marker layer for recovering paleo-geomorphology; the Permian paleo-geomorphology was characterized by “low convex interbedded with groove” during the deposit period of the first member of the Wutonggou formation, which can be further divided into two major grooves and several secondary grooves, while paleo-geomorphology became more gentle after the sediment filling of the second and third members of the Wutonggou formation. Inherited paleo-uplifts and the syn-depositional faults controlled the development of fan deposits. The grooves in the paleo-uplifts are the main factors controlling the direction of paleocurrent and sand body distribution. Huoshen and Qishen syn-depositional faults in the south of the Taibei sag intensify the slope break level between uplift and sag, and the tectonic ridges limit the forward distance of the fan bodies. The “low convex interbedded with groove” control the distribution of the fan bodies. Sand bodies mainly advanced along the paleo-grooves and filled the grooves. During the deposition of the Wutonggou formation, the paleo-geomorphology transformed from the early steep-slope and deep-water fault depression to the late gentle-slope and shallow-water depression.

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    Structural Style and Evolution of Northern Piedmont Belt in Turpan-Hami Basin
    HUANG Diefang, JIANG Menglei, SHAO Manjun, LIN Lin, CHENG Tian, LI Chengming, LIU Juntian
    2020, 41 (6):  651-657.  doi: 10.7657/XJPG20200603
    Abstract ( 444 )   HTML ( 11 )   PDF (1995KB) ( 454 )   Save

    Complex geological structures and poor quality of seismic data make the northern piedmont belt difficult to be explored in the Turpan-Hami basin. In order to make new breakthroughs in oil and gas exploration, geological, seismic and drilling data is used to describe structural styles, conduct structural physical simulation to correct structural interpretation, and establish a more reasonable and accurate structural model to systematically analyze the mechanism and law of the structural deformation in the study area. The results show that double decollement layers (Jurassic coal seam and Permian mudstone) are developed in the northern piedmont belt and thrust nappe structures dominated by imbricated structures form, where zigzag thrust faults, protuberances and imbricated fans can be found vertically. Under the detachment layers, there are double stacked structures or double imbricated structures. In the plane, the piedmont belt is controlled by two groups of faults and the study area is divided into 3 rows of structural belts including thrust belts, overthrust belts and structural belts at the outer edge of the overthrust belts from north to south. The fault anticline and fault-block structural groups in the footwall of the nappe in the middle-east section of the study area are well developed with complete morphology, which are favorable for oil and gas preservation, and are the targets for risk exploration of Jurassic oil and gas. The structural belt at the outer edge of the overthrust belt with relatively complete morphology is a potential target for oil and gas exploration in the Lower Jurassic and its underlying strata.

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    Characteristics and Genesis of Pores in Volcanic Reservoirs of Haerjiawu Formation in Santanghu Basin
    FAN Tanguang
    2020, 41 (6):  658-665.  doi: 10.7657/XJPG20200604
    Abstract ( 354 )   HTML ( 7 )   PDF (10499KB) ( 167 )   Save

    As one of the important methods to study the microscopic pore structure of tight reservoirs, low-temperature nitrogen adsorption experiment has achieved better application in tight clastic reservoirs. This paper takes the Carboniferous volcanic reservoirs in the Santanghu basin as a case to study the genesis of nano-pores in tight reservoirs by applying low-temperature nitrogen adsorption experiment. Experimental analysis shows that the low-temperature nitrogen adsorption curve of the volcanic rock in the Upper Carboniferous Haerjiawu formation of the Santanghu basin is like a “ink bottle”; as the sampling depth increases, the average pore diameter of the samples decreases, the total pore volume increases, the specific surface area increases, and the fractal dimensionality that can characterize the roughness of the pore surface increases too. Further combination with field emission scanning electron microscopy analysis shows that the microscopic pore structure and morphology of the tight volcanic reservoirs of the Haerjiawu formation in the Santanghu basin is related to dissolution. The deeper the reservoir is buried, the more organic acid is produced by the source rock inside the volcanic rock, and the stronger the dissolution is. After unstable minerals such as feldspar are dissolved, new minerals form and then precipitate near pores and throats. This can increase the microscopic pore volume of the reservoirs and reduce their permeability.

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    Spontaneous Imbibition Characteristics of the Shale in Lucaogou Formation in Santanghu Basin
    WAN Yongqing, CAO Xinyu, LIU Haitao, MA Qiang, BAI Zhaoyang, WANG Qi
    2020, 41 (6):  666-676.  doi: 10.7657/XJPG20200605
    Abstract ( 326 )   HTML ( 8 )   PDF (866KB) ( 284 )   Save

    After fracturing in shale reservoirs, the flowback rate of fracturing fluid is low, and the production capacity varies greatly. A large amount of fracturing fluid stays downhole for a long time and is spontaneously inhaled by the reservoir, which has a great impact on oil-gas development and effective production. Based on some related experiments such as shale oil mobility experiment, static spontaneous imbibition experiment and wettability experiment of the shale, etc., the experiment of fracturing fluid displacing oil with the spontaneous imbibition and the experiment of water displacing oil under constant-pressure in shale were carried out, and the unique spontaneous imbibition characteristics were revealed. On the basis of static spontaneous imbibition experiment, starting from the basic physical phenomenon that shale absorbs water, the spontaneous imbibition capacity of shale was reflected by two characteristic parameters on spontaneous imbibition curve, namely spontaneous imbibition saturation and spontaneous imbibition rate. And the flowback curve for producing fluid was analyzed, which was believed that the results of laboratory experiments had a certain predictive effect on fluid production after shale fracturing. Through the liquid-rock spreading experiment, for the shale from Permian Lucaogou formation in the Santanghu basin, the wettability and the influences of the wettability on spontaneous imbibition capacity and on spontaneous imbibition characteristics were analyzed, finding out that the shale had both lipophilicity and hydrophilicity. After analyzing related data comprehensively, it was concluded that the spontaneous imbibition capacity and spontaneous imbibition characteristics of the shale were mainly controlled and influenced by the microscopic pore structure and wettability of the shale.

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    Lithofacies Characteristics and Its Relationship With Shale Oil Reservoirs of Lucaogou Formation in Santanghu Basin
    XU Xiongfei, YU Xiangchun, QING Zhong, ZHANG Yiting, LI Tianjun, YU Haiyue, WANG Bingqian
    2020, 41 (6):  677-684.  doi: 10.7657/XJPG20200606
    Abstract ( 395 )   HTML ( 5 )   PDF (3662KB) ( 361 )   Save

    The shale oil of Lucaogou formation in Santanghu basin is the key exploration target for Tuha oilfield. The researches on lithofacies characteristics and its relationship between lithofacies characteristcs and shale oil reservoirs are lacking, which directly restricts the progress of exploration. The lithofacies type division, fine lithofacies description and lithofacies distribution in the Lucaogou formation of the Santanghu basin are studied through techniques such as core observation, thin section identification, SEM analysis on field emission environment, whole-rock mineral analysis by X-ray diffraction, high-pressure mercury injection and nuclear magnetic resonance. The results show that the reservoir of Lucaogou formation is mainly composed of carbonate, pyroclast and organic matters, and can be classified into massive tuff, thick stratified dolomicrite, laminated tuffaceous dolomite and laminated dolomitic tuff, most of which are medium-rich in organic matter. There are differences in reservoir physical properties, pore-throat structures and reservoir spaces among different lithofacies types. The massive tuff and thick stratified dolomicrite have well-developed pores and good oil-bearing properties, and high yield and sustainable production can be achieved after fracturing. Fractures are well developed in the stratified tuffaceous dolomite, and high yield can also be obtained after fracturing, but cannot be maintained. It is predicted according to the lithofacies distribution that the southern margin of the Tiaohu sag and the Niujuanhu structure in the Malang sag are favorable areas for shale oil exploration.

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    Characteristics and Genesis of Low Oil-Saturation Reservoirs in Taibei Sag, Tuha Basin
    ZHANG Hua, KANG Jilun, WANG Xinggang, LI Hongwei, JIA Xueli, ZHOU Yadong
    2020, 41 (6):  685-691.  doi: 10.7657/XJPG20200607
    Abstract ( 374 )   HTML ( 4 )   PDF (986KB) ( 215 )   Save

    Low oil-saturation reservoirs are widely developed in the Shuixigou group in the Taibei sag of the Tuha basin, which are laterally concentrated in the positive structures in the sag, and vertically in the Xishanyao formation and Sangonghe formation. The oil reservoirs in the study area have low oil saturation and poor physical properties, so the natural productivity is low. Although the production is high after reservoir stimulation, both oil and water are produced for a long time. In order to understand the genesis of such oil reservoirs, the relationships among reservoir, structure, reservoir evolution and oil saturation were studied. The results show that the reservoir and structure are primary factors resulting in the low oil saturation. The reasons are as follows: the first is that the oil displacement by water is not complete due to compaction and pore reduction, fine pores and micro throats; the second is the existence of interlayers or barriers, which separate the oil layers and block the vertical migration of oil and gas; the third is that the low-relief structure provides an insufficient reservoir forming dynamics which will bring impacts on oil saturation; and the fourth is that late tectonic activities destruct the ancient oil reservoirs. Comprehensive analysis shows that the low oil-saturation reservoirs in the Shuixigou group in the Taibei sag have a large amount of remaining hydrocarbon resources, which are important replaceable targets for oil and gas exploration in the Tuha basin. The overlapping areas of reservoir sweet spots and inherited positive structures are favorable for looking for the reservoirs with higher oil saturation.

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    Rolling Evaluation on Small Lithologic Reservoirs in Slope Zones: A Case Study on Putaogou-Pubei Structural Zone of Taibei Sag in Turpan-Hami Basin
    PAN Haifeng, SHU Kun, ZHAO Ronggang, WANG Jie, HOU Chengcheng
    2020, 41 (6):  692-696.  doi: 10.7657/XJPG20200608
    Abstract ( 330 )   HTML ( 5 )   PDF (3038KB) ( 245 )   Save

    The trap with lithologic reservoirs in the structural slope zone superimposes local anticlines or nose-like swells on the slope, which is helpful in blocking oil and gas migrating from the lower part of the slope and making them accumulate in the reservoirs. Usually in nose-like swells or cross-beam slopes in a sag, large delta sand bodies are relatively developed, oil and gas accumulation are controlled by the nose-like swell or ridge-like structure. Low-relief structural traps, lithologic traps and structural-lithologic traps are primary places for oil and gas accumulation. Sandstone reservoirs, connected faults and unconformities are primary channels for oil and gas migration. The lithologic reservoirs developed in the Putaogou-Pubei structural zone are far away from the oil-generating sag and are characterized by subtle structure, small amount of well controlling reserves and difficulties in trap identification. To fully understand various accumulation factors and their relationships is of great significance for rolling evaluation on the lithologic reservoirs in the study area. The reservoirs show rapid lateral changes, strong heterogeneity, and complex OWC, which restrict efficient oilfield development. After comprehensive analysis on the structures, oil reservoirs and reservoir physical properties, the laws of hydrocarbon accumulation are summarized, and the hydrocarbon accumulation model is established for the study area.

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    RESERVOIR ENGINEERING
    Practices and Technology Tackling in Developing Thin Oil Reservoirs in Tuha Oil Region
    ZHOU Bo
    2020, 41 (6):  697-703.  doi: 10.7657/XJPG20200609
    Abstract ( 405 )   HTML ( 11 )   PDF (587KB) ( 198 )   Save

    After 30 years of development, a series of efficient development technologies have been formed for thin oil reservoirs in Tuha oil region. Most of the thin oil reservoirs are of ultra-low to low permeability and very heterogeneous. In the early development stage with low water cut, the reservoirs were developed by powerful oil production and water injection through areal well patterns. During that stage, the oil production was high and the development effect was good. Then in the intermediate stage with medium to high water cut, infilled well pattern was used, which played an important role in slowing down the production decline and stabilizing the production in a short term. However, early powerful production and injection affected the oil displacement efficiency and recovery of the primary pay zones. Especially after entering the late development stage with extra-high water cut, water injection was more and more invalid, and many oil wells suffered from damaged casing or suspending, resulting in low reservoir pressure. It’s difficult to stimulate the thin oil reservoirs by conventional measures, so the development of the thin oil reservoirs was shown as low production rate and low efficiency. In order to fundamentally improve the development effect, Tuha oilfield has actively carried out a series of indoor researches and field pilot tests such as gas injection, composite flooding with nano-micro balls and changing flowing field, made preliminary achievements and formed a series of technologies. With further development and application of these technologies, the natural production decline of the thin oil reservoirs is expected to be controlled from 19.8% to 11.0%, and the recovery is expected to increase by 2.00% to 3.00%.

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    Theoretical Perfection and Application of Tong’s Curve Chart
    CUI Yinghuai, HUI Huijuan, SHENG Han, GAO Wenjun
    2020, 41 (6):  704-708.  doi: 10.7657/XJPG20200610
    Abstract ( 738 )   HTML ( 18 )   PDF (586KB) ( 506 )   Save

    Tong’s curve chart is the primary method for calibrating recoverable reserves in water-flooded oilfields. As water-flooded reservoirs in China produce more and more water one after another, the relationship between recovery percent and water cut in many reservoirs is becoming inconsistent with Tong’s curve. In this paper, on the basis of new seepage characteristic equation, we derive the general formula of Tong’s curve by using Welge equation, and improves the theoretical basis of Tong’s curve. Under certain conditions, the general formula of Tong’s curve can be converted into the typical Tong’s curve and its improved formula, and its corresponding water drive characteristic curve can be converted into Maksimov water drive characteristic curve. Since it can correct Maksimov water drive characteristic curve and Shadrov water drive characteristic curve, the general formula of Tong’s curve is more adaptable under certain conditions. Taking the reservoir of the Sanjianfang formation in Qiuling oilfield as a case, the methods for building actual Tong’s curve and determining reservoir characteristic parameters are proposed.

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    A New Method to Determine Oil-Water Seepage Characteristics in Oil Reservoirs
    JING Wenbo, WANG Rui, LIU Junhui, GAO Wenjun
    2020, 41 (6):  709-713.  doi: 10.7657/XJPG20200611
    Abstract ( 346 )   HTML ( 8 )   PDF (527KB) ( 244 )   Save

    The microscopic oil-water seepage characteristic equation corresponding to the Maksimov-Tong water drive characteristic curve can be obtained by combining differential and material balance equation with Welge equation on the basis of the Maksimov-Tong water drive characteristic curve. It is a new method for determining oil-water seepage characteristics by using production data. Taking the PuⅠ oil reservoirs with good physical properties in Block Nan-2 and Nan-3 of Daqing oilfield as a case, we established the detailed calculation process based on production data, and found the calculated results were almost consistent with water flooding experimental results, indicating that the new method is feasible. Furthermore, the method was applied in the Niujuanhu oil reservoir with extra-low permeability in Wellblock Ma-62 of Santanghu oilfield. But the oil-water seepage characteristics in Wellblock Ma-62 after volume fracturing were very different from the laboratory experimental results obtained from its adjacent wellblocks, indicating that the oil-water seepage characteristics determined in laboratory experiments can only reflect the oil-water seepage characteristics of the basement instead of the porous reservoir during water flooding development.

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    Efficient Development Technologies for Tight Oil in Tuffite Reservoirs in Tiaohu Formation of Santanghu Basin
    YU Jiayi, LI Daoyang, HE Bobin, XIE Shijian
    2020, 41 (6):  714-720.  doi: 10.7657/XJPG20200612
    Abstract ( 325 )   HTML ( 7 )   PDF (981KB) ( 267 )   Save

    The tight oil in the tuffite reservoir of Tiaohu formation in Santanghu basin is distributed stably. The reservoir is characterized by medium to high porosity, ultra-low permeability and high oil saturation and developed natural fractures. Based on the achievements of tight oil exploration in the study area in recent years, technical problems related to efficient development were analyzed. It was found that the technology system of horizontal well plus volume fracturing could stimulate the overall producing of reserves, but the production decline was fast, the primary recovery was low and the development benefit was poor. Finally several technologies were proposed, such as cyclic water injection for rapidly replenishing formation energy, infill wells for reducing well spacing and expanding fracture controlled reserves. After well pattern infilling, cyclic water injection in individual wells was converted to well-group water flooding. Finally, the oil production has been improved in many wells, the recovery has been increased from 2.5% to 10.2%, and the production rate has been kept at 1.0%. Efficient and profitable reservoir development has been realized. The results can be references for developing similar tight reservoirs.

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    Water Injection Development Strategies for the Reservoirs of Xishanyao Formation in
    PAN Youjun, XIE Jun, MENG Pengfei, YANG Zhen, YANG Yongxia
    2020, 41 (6):  721-728.  doi: 10.7657/XJPG20200613
    Abstract ( 327 )   HTML ( 4 )   PDF (2259KB) ( 181 )   Save

    The reservoirs of Xishanyao formation in Niujuanhu block of Santanghu oilfield are sandstone reservoirs with the characteristics of low permeability, low pressure and low mobility. In the early stage of development, there were problems such as poor water injection effects, low production of oil wells, and etc. In order to improve development effects of water injection, through the analysis of production performance statistics and the study on reservoir engineering and simulation methods, the technical and strategic limits for water injection were redefined, and the moderately advanced water injection was implemented. Meanwhile, reasonable well patterns and well spacing were discussed, the adjustment and the infilling in well patterns were implemented, and the favorable areas were depicted to prepare for rolling production. After the implementation of a series of strategies, the water injection development status for the reservoirs of Xishanyao formation in Niujuanhu block has gradually become better. At present, the reservoir pressure stays stable, the water content is controlled within 55%, and the natural decline rate of oil production drops to about 10%. The oil production remains stable and the maximum oil production rate can reach as high as 1.04%, which is still above 0.70% currently. It is predicted that the oil recovery rates of the southern and eastern areas of the reservoir in Xishanyao formation in the Niujuanhu block are 24.5% and 18.1%, respectively, both of which are higher than 18.0% calibrated in the development plan.

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    Adaptability Evaluation of Nitrogen Foam Flooding After Water-Flooding in Low-Permeability Light Oil Reservoirs
    XIAO Zhipeng, YANG Shenglai, MA Xueli, HAN Jifan, WANG Mengyu
    2020, 41 (6):  729-734.  doi: 10.7657/XJPG20200614
    Abstract ( 336 )   HTML ( 8 )   PDF (562KB) ( 197 )   Save

    After water-flooding development, the low-permeability light oil reservoirs have entered a stage of high water cut, and the reservoirs have been seriously water-flooded in Tuha oilfield, so no water flooding measures seem effective. To improve the recovery, it is urgent to find other EOR technologies. Since high-viscosity fluid (i.e. polymer) is not applicable for the low-permeability reservoirs, laboratory experiments were carried out to investigate the oil displacement efficiency and its influencing factors based on water flooding, nitrogen foam flooding and nitrogen foam flooding after water flooding. The experimental results show that the oil displacement efficiency by water flooding increases with the increase of reservoir permeability and has a better logarithmic relationship with the permeability; the nitrogen foam flooding efficiency is 67.66%, which is 10.62% higher than that of water-flooding; nitrogen foam flooding after water flooding can improve the oil displacement efficiency by about 9.63% on the basis of water flooding. The residual resistance factor of the foam used in the experiments is greater than 1, which indicates that the recovery after water-flooding has been increased by using nitrogen foam with water plugging and profile modification. It is concluded that the nitrogen foam flooding is suitable for the low-permeability light oil reservoirs according to its mechanism and experimental results in Tuha oilfield.

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    Stereoscopic Waterflooding Technology and Its Application in Niudong Volcanic Oil Reservoir
    WU Mei’e, ZHANG Zhongjin, ZHANG Mei, PAN Youjun, XIE Shijian, CHEN Changxu
    2020, 41 (6):  735-739.  doi: 10.7657/XJPG20200615
    Abstract ( 324 )   HTML ( 6 )   PDF (1258KB) ( 300 )   Save

    Niudong volcanic oil reservoir is a kind of special oil reservoir of abnormal temperature and normal pressure. It was formed by multiple stages of volcanic eruption, so the reservoir is on a small scale. In the reservoir, there are developed fractures that are dominated by almost low-angle and horizontal cracks, and oil layers cover a large span vertically, and each layer is very thick and heterogeneous. During the early development, rapid production decline occurred in the wells developed by depletion method; water flooding pilot test was carried out in vertical well groups, the daily oil production of adjacent wells increased slightly; and the EOR result of cyclic water injection pilot test in horizontal wells was not very good, indicating that the waterflooding effect was not oblivious. Regarding these problems, a vertical-horizontal well-mixed, stereoscopic waterflooding technology has been established based on the optimizations of cyclic water injection, well pattern adjustment and fracturing program, which can effectively improve the waterflooding effect in volcanic oil reservoirs. The actual application of the technology in horizontal wells exhibits a good effect with the well response rate of 44.4%, the initial incremental oil production of 1.7 t/d per well, and the expected enhanced oil recovery of 5.7%, which can provide references for the development of the other similar oil reservoirs.

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    APPLICATION OF TECHNOLOGY
    Progress of Well Logging Evaluation Techniques for Shale Oil of Lucaogou Formation in Santanghu Basin
    HAN Cheng, CHEN Xuan, CHEN Jie, YIN Xueqi, ZHANG Rigong, GENG Ziyuan, PENG Yazhong
    2020, 41 (6):  740-747.  doi: 10.7657/XJPG20200616
    Abstract ( 362 )   HTML ( 9 )   PDF (708KB) ( 266 )   Save

    The shale oil reservoirs of the Lucaogou formation in the Santanghu basin have complex lithologies, various types of reservoir space, and unknown source-reservoir configuration relation, thus the characteristics and distribution rule of sweet spots are unclear. Through calibrating well logging data by core, the well logging data are used to calculate and evaluate the total organic carbon content and hydrocarbon generation potential, then high-quality source rocks in the basin are the classified and evaluated. Reasonable T2 cutoff value and starting time are determined by NMR logging data, the effective reservoirs and oil-bearing property are evaluated according to different grades and types of pores, and the classification and lower limit standards of effective reservoirs are established. Through multi-well comparison and logging-seismic combination, the mutual distribution between source and reservoir and the characteristics of lamellar development are clarified, and the well logging response characteristics and longitudinal distribution of sweet spots are defined. The research results provide a basis for the prediction of shale oil sweet spots and the optimization of favorable zones. The shale oil production capacity construction and efficient producing in Block Tiao 34 and Block Niujuanhu have been realized.

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    Application of Hypoxic Air Huff and Puff Technology in Deep Heavy Oil Reservoirs in Lukeqin Oilfield
    GAO Neng, ZHAO Jian, HE Jia
    2020, 41 (6):  748-752.  doi: 10.7657/XJPG20200617
    Abstract ( 368 )   HTML ( 14 )   PDF (1035KB) ( 257 )   Save

    Over many years of oilfield development by waterflooding, problems such as rapid rise of water cut, low waterflooding efficiency and low recovery percent of reserves have been encountered in deep heavy Triassic oil reservoirs in Lukeqin oilfield. In order to improve waterflooding development effect and increase well production, a hypoxic air huff and puff program was put forward. Then based on laboratory physical simulation experiments and numerical simulation, the mechanism of hypoxic air huff and puff was analyzed, and waterflooding parameters were optimized. Finally taking the deep Triassic heavy oil reservoirs in Lukeqin oilfield as a case, a field test of hypoxic air huff and puff was carried out. The results show that the mechanism of increasing oil production through hypoxic air huff and puff is that a pseudo bubble point would appear after injecting hypoxic air into heavy oil reservoirs, and the heavy oil changes to foam oil which can reduce the viscosity of crude oil and block dominant water channels, as a result expanding the sweeping volume. Air injection rate and volume and soaking time have great influences on the effect of hypoxic air stimulation. It is suggested that the injected gas volume should be about 400, 000 m3, injection rate should be 40, 000 m3/d, and soaking time should be 8-10 days in a single well. Hypoxic air huff and puff has been implemented in the deep Triassic heavy oil reservoirs in more than 400 wells in Lukeqin oilfield, among which 82% of the wells are effective, namely, the oil production increases by 4.5 t/d per well and water cut decreases by 42% at the initial stage; the valid period is 168 days and the cumulative oil production has been increased by 480.0 t per well. These results have proved that hypoxic air huff and puff is an effective technology for increasing oil production while decreasing water cut for deep heavy oil development. These findings are important references to improving oil recovery of similar reservoirs after experiencing waterflooding development.

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