Reason Of Sandstone Reservoir Sensitivity In Wangzhuang-Ninghai Areas

Based on multiple methods of test, and combining with reservoir sensitivity tests, the characteristic of clay minerals of clastic reservoir of Zhengjia -Wangzhuang area are systematically studied, and the reason of reservoir sensitivity was discussed.Lying on the north actic region of Dongying Sag, the aimed area was controlled by Chennan fault and palaeogeomorphic fluctuation of convex limb of Chenjiazhuang bulge, and the area developed Sha-4, Sha-3 and Sha-1 Formation in Paleogene. Lots of glutenite bodies of alluvial fan in Sha-4 sedimentary period, and of fan delta developed in Sha-3 and Sha-1 sedimentary period. Thus, superimposed multi-thick bedded reservoir formed on vertical direction which was characterized by complicated lithology, low compositional maturity and texture maturity, weak diagenesis, high reservoir quality, high heterogeneity and high shale content.X-ray diffraction analysis shows the clay minerals in the sandstone reservoir is composed of randomly interstratified illite/montmorillonites (S/I), kaolinite, illite and chlorite in which the quantity of randomly interstratified illite/montmorillonites and kaolinite are much more than the others, and the former one's rate of montmorillonite to illite lay is more than 80 percent. There are two kinds origins of kaolinite that are high crystalline authigenic one and low crystalline allogenic one which developed mainly in Sha-1 Formation. S/I can subdivide into three kinds: calcium type, natrium type and calcium-natrium mixture type according to the cations' type in the interlays, in which calcium -natrium mixture type is more than the others. S/I exhibits two morphological habits: honeycomb and net. Additionally, illite and chlorite exist in small amount, the former one exhibit silk or bridge intergranular filling, and the later nearly can't see in microscope.In order to improving calculate accuracy of total amount of clay in clastic reservoirs, on the basis of experimental analysis, a new method, twice grain size segregation plus x-ray diffraction of randomly oriented powers of clay minerals, was put forward to calculate the total amount in clastic reservoir rock. Contracting with other methods, the one was characterized by simpler processing, good theorization, strong representativeness and higher precision.In order to analyze the reason of reservoir sensitivity, Measurement to sample's cation exchange capability (CEC) and swell capability (SC) in solvent indicates that CEC and SC of clay minerals in Sha-1 Formation are more than ones in Sha-3 Formation. And the course of cation exchange is the course of swelling, Swell capability and CEC have positive linear correlation with the relative quantity of S/I. Measurement to reservoir sensitivity indicates that water-sensitivity and velocity-sensitivity are the main sensitivity kinds of clastic reservoir of the areas, and the main kinds of clastic reservoir sensitivity in Sha-3 Formation main are water-sensitivity and velocity-sensitivity which is relative weak. And in Sha-1 Formation main is water-sensitivity which is relative strong. Additionally, on the basis of routine drilling core experimental analysis, taking use of multiple well logging data, the types of clay minerals, the total amount of clay and sensitivity index are calculated, and forecasting models has been established, the sensitivity evaluation of all-well and the whole area have been accomplished.The controlling factors to reservoir velocity-sensitivity are reservoirs quality and total amount of clay in clastic reservoirs, and to water-sensitivity is the content of S/I. In the course of thermal recovery, S/I, having the similar character with montmorillonite, can swell acutely which can cause formation damage of the reservoir.