The Evaluation On Reservoir Sensitivity Of Changjiaweizi Regoin In Songliao Basin

Changjiaweizi , located in the central depression of Songliao Basin,its main body is located in the Qijia-Gulong two level formation. There developed the Gaoxi Formation under the west monocline and the main oil-bearing horizon is Putaohua Formation which lied in the main part of the formation.The test research indicated that the formation is low filter reservoir that has the characteristics of small granule,bad sorting high content of cementation and mud,complicated structure of hole , so it is very important to protect the reservoir. Changjiaweizi area has not been system appraisaled the reservoir sensitive until now .Therefore, it is necessary to develop rock mineral test and reservoir sensitivity experiment and take system appraise of reservoir sensitivity, then confirm the reservoir sensitivity and the impact factors.According to analysis of appraisal of rock flake,X- diffraction and scanning electron microscope (SEM), we can know that the reservoir of Changjiaweizi Formation formed in subaqueous fan and fan-delta facies. Feldspathic and lithic sandstones are the main rock types, of which the content of instable components feldspar and debris are high, the contain of quartz 35%, feldspar 25% and debris38% average. The main types of clay mineral includ, illite, illite-montmorillonite, kaolinite and chlorite. And the main carbonate mineral is calcite, with a little dolomite and ankerite.The main function of Changjiaweiji reservoir is carbonate cementation action and clay mineral cementation action, and the contain of carbonate cementation can research 47.8%, which main includes calcite,with little dolomite and ankerite. The main component of clay mineral is 33.31% illite-montmorillonite , 33.12% illite , 26.6% kaolinite , and 6.97% chlorite, and the whole contain of clay mineral can reach 13%～30%,18.8% average. It is easy for physical and chemical reaction to take place and lead to reservoir damage of potential velocity, alkali, water, and acid sensitivity.According to statistics of porosity and permeability, reservoir is mid&low porosity and low permeability. Indicated by mercury injection curve, the pore throats are small, the distribution of pore is asymmetric and pore texture is complex. Low porosity, low permeability and complex pore texture have reinforcing effect on water sensitivity, but have weakening effect on velocity sensitivity. In addition, the potential reservoir damage is related to formation fluid property in the research area.This article used sensitivity experiment to evaluate potential damage of water, salt, alkali, acid and stress sensitivity quantificationally. most exponents of sample of reservoir acid damage are above 50, which are mid-strong degree damage. In salt sensitivity experiment, permeability declines rapidly when the salinities of experiment fluid change. During acid sensitivity experiment, most exponents of sample of reservoir acid damage are about 25.Alkali sensitivity experiment indicated exponents of alkali damage is low, which shows that there are less-degree alkali sensitivity damages. Therefore, we can know that the primary types of reservoir damage are water sensitivity and acid sensitivity, stress sensitivity. Water sensitivity damage is mid-strong, and alkali damage sensitivity is less-degree.According to analysis of clay minerals, the main reason for reservoir damage is illite montmorillonite and illite, because illite montmorillonite is the most expanded minerals in clays of this area. And with the contents of illite montmorillonite increase in water sensitivity experiment, the degrees of water damage also strenthen. Because, in all clays, kaolinite has the highest activtiy reacted with alkali, mainly alkali senstivity damage is related to kaolinite. Acid damage is related to carbonates.Finally, author provided measurement to prevent reservoir damage and promote oil-gas production according to the characteristics in the study area. Clay stabilizer has marked restraining role on water sensitivity damage of reservoirs; it is effective to use temporary blocking technique to prevent alkali damage; The effective measure to prevent acid damage is to keep pH lower. We can maintenance pressure to prevent stress damage.