The Study On The Reservoir Characteristics And Favorable Area Prediction Of X₂ Reservoir Of Xishanyao Formation In Niuquanhu Area, Santanghu Basin

Xishanyao formation oil reservoir of Niuquanhu area in Santanghu basin possesses a typical "three-low" characteristics-low permeability、low pressure、low mobility, which makes the complex macroscopic internal construction and the complex microscopic pore structure and seepage mechanism of the reservoir of Xishanyao formation. Series of problems appeared in the process of exploitation,such as quick injection-production effect1the fast falling fluid and oil productivity index、low recovery degree andso on. In order to improve reservoir exploitation effect, first a comprehensive analysis has been made from the macro including different types of reservoir sedimentary microfacies types and distribution characteristics, petrological characteristics, physical characteristics, diagenesis, etc; Then an in-depth research has been made on the microscopic pore structure of the reservoir and seepage mechanism, finally combining with dynamic production data, a comprehensive evaluation has been made for all kinds of reservoirs.Main findings have been got as follows:1. The X2 reservoir of Xishanyao formation of the studied area belongs to sedimentary subfacies of fan delta front, the main sand body is in the ribbon, the whole sand thickness is small, the subject in the study area is a wide and gentle anticline.The reservoir is mainly composed of feldspar lithic sandstone, the highest content in the clastic particles is debris, and contains much interstitial material, clay mineral is mainly kaolinite. Granularity is mainly for fine and medium grained, with medium particle separation and good rounding, particles is mainly with point-line, line contact. The compositional maturity and textural maturity of the sandstone are on the low side as a whole.2 The pore type of the X2 reservoir of Xishanyao formation of the studied area are mainly composed of residual intergranular pore、tuffaceous solution pore、feldspar dissolved pore,etc. also partly composed of the micro crevice, and the main pore combination type are composed of inter-grain hole-dissolved pore、the intergranular hole-dissolved pore、 micropore,etc; Throat type of X2 reservoir of the studied area is maily dot thtoat. On the whole, the development of pore throat is poor, and capillary pressure curve are mainly type Ⅱ and type Ⅲ; Constant speed mercury injection experiments shows that total pore throat mercury-injection saturation is mainly decided by the throat, this is because throats provide huge storage space for the reservoir of the study area, at the same time, a large number of intergranular hole formed by kaolinite makes a great contribution to the throat mercury-injection saturation.3. The X2 reservoir of Xishanyao formation of the studied area has a poor reservoir property、 high interstitial material content、 complex microscopic pore structure, etc, as a result, the irreducible water saturation of the reservoir is high, the average is 35.13% by oil and water relative permeability test, two phase seepage area is small, nuclear magnetic resonance shows that the movable fluid saturation of the X2 reservoir of Xishanyao formation is only 48.41%, and the whole seepage ability is poor.4. The oil-water distribution of X2 reservoir of the studied area on macroscopic is controlled by sedimentation, diagenesis, tectonism together, on the microscopic it is mainly controlled by the pore structure characteristics and seepage characteristics; Based on the comprehensive analysis on the characteristics of X2 reservoir of Xishanyao formation, the reservoir of X2 can be divided into four categories, the storage capacity and seepage ability of type I and II reservoir is good, these two types of reservoir are the main reservoir types of favorable evaluation areas for prediction.