In order to understand the development characteristics of the dominant water flow channels in the North Buzachi oilfield, the dominant water flow channels in the target layers in Block VI of the oilfield were identified by using streamlined numerical simulation technology, and the development degree and formation pattern of the dominant water flow channels were quantitatively characterized. The results show that Class Ⅰand Ⅱ channels in the study area are the water flow channels with ineffective circulation, with water flooding sweep coefficient of only 0.120-0.175. For Class I channels, the water cut at the producer is greater than 97%, and the average sweep coefficient is 0.120, with extremely serious channeling. For Class II channels, the water cut at the producer ranges from 93% to 97%, and the average sweep coefficient is 0.175, with serious channeling. The dominant water flow channels are small in number and limited in volume, but they occupy most of the water volume, which results in inefficient water injection. The number of dominant channels is inversely proportional to the distance between injector and producer. The location of the main river channel is the main area where the dominant water flow channels are formed, especially in the direction that the connection line between the injector and the producer is parallel to the sedimentary direction of the main river channel. The longer the producing time of the producer and injector, and the higher the ratio of cumulative liquid production to water injection, the higher the probability of dominant channel occurs near the wells with high daily liquid production. Furthermore, the dominant water flow channels change with the initial production time of the producer and the adjustment of injector-producer relationship.
The Cretaceous low-resistivity oil layers in WTK oilfield, South Turgay basin are widely developed and difficult to identify. In this paper, the genetic mechanism of these low-resistivity oil layers was analyzed using core analysis and logging data, and the method for identifying oil/water layers was stuided by combining formation testing data. According to the geological features of the study area, comprehensive research was carried out on internal factors and external factors. The internal factors include the reservoir lithology and clay mineral content during the deposition process, the pore structure characteristics and fluid distribution during diagenesis, and the oil-water differentiation during hydrocarbon accumulation, and the external factors include the accuracy of measurement methods during drilling, etc. The main controlling factors for the low resistivity of the oil layers in the study area are the additional conductivity of clay mineral cations and the conductivity caused by high irreducible water saturation and salinity, and the secondary controlling factors are low structural amplitude and thin oil layers. By analyzing the reservoir conductivity model and based on the model for calculating formation water and irreducible water saturations, the relationship between electrical characteristics and fluid saturation was established, the quantitative evaluation model of low-conductivity oil layers was constructed by stratification, and the lower limit standard for dividing each fluid type was made to realize accurate fluid identification. The practical application shows that the matching degree between the results of logging interpretation and actual production reaches 88.2%, suggesting a good application effect.
In the late high-water cut stage in KS oilfield, profile control in water injection wells is a common measure to stabilize oil production while controlling water production. However, it is difficult to decide index limits and quantify weight values when selecting water wells. This study screened single-well, interwell and static indicators that can accurately reflect the characteristics of water channeling, developed a new kernel function based on polynomial kernel function, radial basis kernel function and Sigmoid kernel function, and optimized the fuzzy clustering method to improve the accuracy of fitting and prediction. Then a special fuzzy clustering method was proposed for selecting wells for profile control in the late high water-cut stage in KS oilfield. It can improve the recognition rates of sample set and detected set for selected wells. The new decision-making method for selecting wells for profile control has been applied to KS oilfield, and 3 wells were selected from 22 water wells for profile control. Significant oil increasing and water reducing effects have been achieved.
In order to evaluate the sealing ability of the Lower Cretaceous mudstone caprock in the D basin in Chad, the thickness, porosity, and break-out pressure of the mudstone caprock are obtained by using well logging data; the relationship between break-out pressure and interval velocity, and the relationship between mud-to-formation ratio and seismic attributes are analyzed; the plane distribution of break-out pressure and mudstone thickness are described; and the evaluation standard for the grading of the mudstone caprock is established by taking break-out pressure and mud-to-formation ratio as primary evaluation parameters. The results show that the mudstone in the Kedeni formation in the D Basin is classified into Type Ⅰ and Ⅱcaprocks, and the mudstone in the Doba formation is Type Ⅱ and Ⅲcaprocks. The sealing ability of the mudstone caprock in the Kedeni formation is stronger than that in the Doba formation. On plane, the mudstone caprocks in the northern steep slope zone and sags have the best sealing abilities, and are ranked as Type Ⅰ and Ⅱ, followed by the mudstone caprocks in the central low-amplitude uplift zone and the southern gentle slope zone, which is dominated by Type Ⅱ and Ⅲ, and the worst mudstone caprock is in the northeastern transition zone, which is Type IV. The evaluation results are in good agreement with the actual drilling results, indicating that the evaluation method is effective and provides a good reference for mudstone caprock evaluation in similar basins with relatively low exploration degrees.
In order to further characterize the structure and fractal characteristics of different pore throats in tight sandstone reservoirs, the tight sandstone samples from Upper Montney formation in Block A of western Canada sedimentary basin are studied by using cast thin section, SEM and high pressure mercury injection analyses. The results show that the pore types of the reservoir in the study area mainly include dissolution pore, primary residual intergranular pore and intercrystal micropore, and a small number of microfractures are noted. Most of the pore throat radius of the reservoir is less than 0.30 μm, showing a curve with multiple peaks, and the effective storage space is mainly composed of nano- and submicron- pores. The tight sandstones in the study area can be divided into Type Ⅰ, Type Ⅱ and Type Ⅲ with the corresponding average overall fractal dimensions of 2.31, 2.46 and 2.63, respectively. The Type I samples have relatively good physical properties and relatively weak heterogeneity. The fractal characteristics of pore throats with different sizes are different. The fractal dimension of the submicron pore throats is higher than that of nano pore throats, indicating a stronger heterogeneity of the submicron pore throats. The fractal dimension of pore throats is related to pore throat structure, and the development of different pore throats in tight sandstone reservoirs results in different heterogeneity of pore throats.
