储层压实作用和胶结作用的压力响应特征

为了在发育异常高压沉积盆地的中深层进行有效的油气勘探,综合运用薄片、岩心常规、粒度分析、SEM等分析化验资料,探讨了渤中凹陷西北次凹储层压实作用和胶结作用的压力响应特征。得到了异常高压对机械压实具有抑制作用的有力证据。证实了不同胶结物类型有不同的压力响应特征。研究认为,每超静水压力7 MPa的异常高压可保存约2.0%原生孔隙。胶结强度的压力响应特征呈斜坡状:1陡坡段,远离高压界面的常压带→高压界面外280 m,胶结强度迅速增强,以弱胶结为特征,胶结物以自生黏土矿物为主,约占总胶结物的85%;2缓坡段,高压界面外280 m→异常高压带,胶结强度缓慢增大,以强—中胶结为特征,胶结物以碳酸盐为主,约占总胶结物的75%以上。在高压界面附近的常压带,碳酸盐胶结作用的压力响应厚度比自生黏土矿物的响应厚度小,前者约280 m,后者430 m。研究区原生孔隙与渗透率具有较好相关性,相关系数可达0.77,表明原生孔隙发育的砂岩是优质储层。研究结果可为在异常高压发育的盆地中深层寻找优质储层提供理论依据。

Characteristics of Pressure Response in Detrital Resveroir Compaction and Cementation

In order to raise up success rate of oil & gas exploration in mid-deep sedimentary basin with overpressures, characteristics of pressure response in reservoir compaction and cementation in Dongying formation in Northwestern Bozhong sag was studied, based on a lot of data from thin section, core analysis, grading analysis, SEM, etc. Strong evidence was obtained to testify that detrital reservoir compaction was inhibited by overpressures. In addition, it was not only proved that both carbonate and authigenic clay would be prompted by overpressures, but also indicated that this two types of cementation had disparate characteristics of pressure response in study area. The results showed that primary pore could be preserved about 2.0% as pore pressure was above hydrostatic pressure every 7 MPa in overpressures setting. With response to overpressure, cementations strength changed typically in scarp shape as depth increased: ①Abrupt slope stage from the less depth to 280 m outside of overpressures interface, where cementation strength swiftly increased, was characterized by weak cementation strength, whose cementation was dominated by authigenic clay with about 85%; ②Gentle slope stag from 280 m outside of overpressures interface to overpressures zone, where cementation strength slowly increased, was characterized by strong-middle cementation strength,whose cementation was mainly occupied by carbonate cementation with over 75%. In normal pressure zone close to overpressures, influenced depth of carbonate cementation with response to overpressures was obviously shallower than that of authigenic clay minerals, the former was about 280 m and the latter was over 430 m. The correlation between residually primary pore and permeability was well in study area, whose coefficient could be near 0.77. It indicated that sandstone with a number of primary porosity could be effective reservoir in mid-deep strata. The research can be taken as theoretical basis for oil & gas exploration in mid-deep strata of sedimentary basin with overpressures.