Chlorite coats are widely recognized as a key element in preserving sandstone porosity because it can inhibit the growth of quartz cements. However, the alteration of chlorite coats and its potential influences on sandstone porosity are rarely discussed. Therefore, this work used reactive transport models under different petrographic and geochemical conditions to investigate the influence of chlorite coats on sandstone porosity in a major dissolution window (100 degrees C). The HCO3-rich (CO2-charged) and HCO3-depleted (organic acids-charged) waters were injected to induce mineral dissolution and precipitation. The results indicate that the alteration of chlorite coats may result in sandstone porosity reduction. The HCO3-rich water leads to a porosity decrease mainly through the precipitation of magnesite and siderite resulting from chlorite dissolution. In contrast, the HCO3- depleted water causes a porosity decrease mainly through the redistribution of kaolinite and quartz cements. Factors, including pCO2, organic acid concentration, coat coverage, coat thickness, and grain size, have secondary influences on net porosity change. In comparison, factors, including chlorite mineralogy, detrital lithology, and the reduction of K-feldspar dissolution rate caused by chlorite coat, have negligible influences. The alteration of chlorite coats may introduce significant mis-interpretation to the analysis of the relationship be-tween chlorite coats and sedimentary facies. Moreover, the actual impact of pore-filling chlorite on porosity reduction may be either underestimated or overestimated. Therefore, the alteration of chlorite coats should be taken into consideration in future studies.

对研究区千余口单井建立声波时差压实曲线,利用等效深度法计算泥岩超压值,结合DST和RFT实测资料以及地震资料,综合考虑研究区沉积及构造特点,最终揭示了松辽盆地齐家古龙凹陷—三肇凹陷中浅层地层存在4套压力体系,即嫩二段以上的常压体系,嫩江组一段、二段弱超压体系,姚家组常压、低压和弱超压并存体系以及青山口组超压体系。不同层位异常压力分布范围和规模不同,其中青一段最为广泛。产生异常压力的原因复杂:超压形成主要受泥岩欠压实和油气生成控制,嫩江组末期的构造抬升作用是研究区产生异常低压的主要原因,而超压流体流动导致的压力传导作用为压力的再分布提供了有力条件。

Based on abundant logging data, combined with DST, RFT data and rare sesmic information, comprehensively considering the feature of deposition and structure, the research establishes more than one thousand acoustic interval transit time curves and fluid pressures are calculated by equivalent depth method and the characteristics of abnormal pressure distribution are revealed in study area. The results indicate: 1) Overpressure is prevalent in study area, and Qijiagulong depression, which is one of the most important oil-bearing depression, has the most extensive area and largest overpressure value. 2) Vertically, there are four pressure systems. The formation above K 2n 2 is normal pressure, and K 2n 2-K 2n 1 and K 2qn formation develop overpressure. However, K 2y formation, which is between K 2n and K 2qn, simultaneously has normal and abnormal pressure. 3) More than one mechanism should be responsible for abnormal pressure genesis. Disequilibrium compaction and hydrocarbon generation are the main causes of overpressure. Tectonic uplift during the end of Nenjiang Formation leads to the abnormal low pressure in Yaojia Formation. Eventually, transit pressure causes by fluid flow redistributes the abnormal pressure.