渤南洼陷沙四段膏岩层发育与地层异常压力的关系分析

THE RELATIONSHIP BETWEEN GYPSUM-SALT LAYER AND STRATIGRAPHIC ABNORMAL PRESSURE OF THE Sa4 MEMBER IN THE BONAN SAG

运用油气蔵动力学理论,针对渤南洼陷沙四段储集层进行岩石学(岩石薄片123片)、储集性能(岩心孔隙度测试145块)分析测试,结果表明:渤南洼陷沙四段中的膏岩层主要发育于洼陷的中部,厚度最大可达百余米,岩性以灰白色石膏岩、泥膏岩和深灰色石膏质泥岩为主,其与泥岩、泥质粉砂岩交互出现。储层物性以渤南断裂带最好(平均孔隙度9.8%),深洼陷带次之(平均孔隙度9.4%),纵向上膏岩层间和膏岩层下发育1~2个次生孔隙发育带(3 330m^3 630m,3 730m^3 830m)。利用测井资料计算地层压力表明,埕南断裂带沙四上亚段压力系数为0.93~1.12,平均1.04,属于常压系统。深洼陷带压力系数为1.2~1.7,深洼陷带属于高压系统。渤深断阶带,沙四上亚段压力系数为1.2~1.6,属于高压系统;下亚段压力系数为1.1~1.4,为弱-中超压系统。膏岩层的存在使超压体系产生明显差异,渤南洼陷的中强超压主要出现在沙四段顶部的膏岩层之下,而未发育膏岩层的地区沙四段则为常压。综合分析认为渤南洼陷膏岩层的发育是造成各构造区块沙四段储层物性差异的原因之一。异常压力对储层物性具有强烈的影响和控制作用,超压与深部物性较好的储层在纵向和平面上均能相匹配。

Dynamic theory of oil and gas reservoir is used to study the petrology, accumulation performance and temperature ＆ pressure conditions of strata for the Sa4 member in the Bonan Sag. It shows that the thickness of gypsum-salt layer occurred in the middle part of the sag reaches up to several hundred meters and composed of gypsum, mud paste rock and heavy gray colored gypsum mudstone,intercalated with mudstone and pelitic siltstone. The physical property of reservoir along the Bonan fault is the best with an average porosity of 9.8%, and the physical property of reservoir in the deep sag comes the second with an average porosity of 9.4%. Within the gypsum-salt layers and below the gypsum-salt layer,there are one to two secondary pore belts （3 330 m～3 630 m and 3 730 m～3 830 m）. Homogenization temperature obtained from inclusions is in the range of 110℃～160 ℃ with 2 peak values of 120 ℃～130 ℃ and 140℃～150 ℃. Calculation of strata pressure indicates that the existence of gypsum-salt layers leads to the obvious difference of ultra high pressure system. Ultra high pressure mainly occurs beneath the gypsum-salt layers in the upper Sa4 member, while in the area without the development of gypsumsalt layers,the Sa4 member remains ordinary pressure. It is considered that the development of gypsum-salt layers in the Bonan sag is responsible for the difference of physical property in the Sa4 member. Abnormal pressure remarkably affects and controls the physical property of reservoir. The ultra high pressure and deep developed good reservoir accompany each other both in plane and in profile.