Fluid Identification Of Low Permeabity Sandstone Reservoir In Jilin Oilfield

In this paper, based on modern hydrocarbon reservoir generation theory and hydrocarbon system idea, started with the basic geologic condition of the hydrocarbon reservoir generation, selected the typical reservoir to study, the forming mechanism and geologic conditions of the low permeable reservoir are pointed out. Using the comprehensive analysis for geologic, well logging, oil testing and other test and analysis data, the low permeable reservoir fluid is recognized. Based on study, the common reasons of the low resistivity reservoir generation are as follows:① they are all located in the depositional microfacies of the river mouth bar, distal sandbar and sheet sand located in fan delta frontal subfacies; ② the rock grain is fine (the medium grain size is generally less than 0.07mm), the muddy content is high (>15%), the lithology is fine siltstone, muddy siltstone and silty mudstone, the rock pore structure is complicated; ③ the clay mineral content is high, which is mainly illite and illite/smectite mixed layer (>70%); ④ the reservoir bound water content is high (>20) . There are also some special reasons: ① the micropore and the secondary pore are developed, which has a double pore/fracture system of intergranular pore- fracture; ② the reservoirs are Low – Amplitude Structural Reservoirs, the height of the reservoir is small, the oil and water transition belt is wide and the water bearing saturation of the oil formation is high; ③ the salinity of the formation water is high ( or low); ④ well logging factors (e.g. Fang 44, Fang 54); ⑤ the rock contains locally metal minerals which have better conductibility. The quantitative interpretation model for evaluating the low resistivity reservoir parameters of the central depression area in the south of Songliao basin is established through the rock physical experiment , such as recompression porosity, recompression permeability, recompression interval transit time, electrical property of rock under high temperature and pressure, capillary pressure, clay additional conductibility, rock resistivity of formation water with multi-salinity saturation, cation exchange capacity, relative permeability and nuclear magnetic resonance and so on. On the basis of analysis to the generation conditions of the low resistivity reservoir, the main mechanism of the low resistivity reservoir generation is understood. It is considered that the high content of the bound water and clay minerals are the main factors for the low resistivity reservoir generation. For the characteristics of high clay minerals content of the low resistivity reservoir, a muddy correction to the deep resistivity is made. An electric property chart for low resistivity reservoir recognition is firstly established in the south of Songliao basin, and the water and oil resolution of the low resistivity reservoir is improved. For the regular reservoir, the fluid property can be estimated by the background value of the Archie formula, but for the low permeability reservoir, the wrong oil and water formation recognition is often made by only using the background value to recognize the fluid, compared with the oil test data, the coincidence rate is low. When using the regular well logging data to recognize the oil and water formations of the single well of the low permeability reservoir, it must be under the background value conditions combined with the following recognition methods: 1. differential identification; 2. no invasion line method; 3. SP (spontaneous potential) "deviation" phenomenon; 4. fluid recognition method for exploration well; 5. resistivity increase method; 6. reservoir comprehensive evaluation method...