古龙页岩油富集因素评价与生产规律研究

Shale oil enrichment evaluation and production law in Gulong Sag,Songliao Basin,NE China

基于大量钻井、分析测试、模拟实验,对松辽盆地古龙凹陷白垩系青山口组页岩(古龙页岩)的生烃演化、页岩油赋存状态、孔缝演化机制进行深入分析,并结合大量试油试采资料,开展古龙页岩油富集层评价、生产特征与产量递减规律分析。研究表明:(1)古龙页岩在Ro值为1.0%~1.2%时进入大量排烃期,最大排烃效率为49.5%;中低演化阶段,页岩油的主要赋存空间从干酪根向岩石与有机孔缝转移;中高演化阶段,页岩油由吸附态向游离态转化。(2)孔隙类型主要为黏土矿物晶间孔缝、溶蚀孔和有机孔,黏土矿物转化过程中在伊利石、伊蒙混层矿物间形成大量晶间孔缝,有机质裂解作用形成网状孔缝。(3)游离烃含量、可动孔隙度、总孔隙度、脆性矿物含量是页岩油富集层分类评价的核心指标参数,Ⅰ类层标准为S_(1)≥6.0 mg/g,可动孔隙度大于等于3.5%,总孔隙度大于等于8.0%,脆性矿物含量大于等于50%,综合认为Q2—Q3、Q8—Q9油层最优。(4)轻质油带核心区水平井首年累产高,属于双曲递减模式,递减指数一般为0.85~0.95,首年递减率为14.5%~26.5%,单井预测可采储量(EUR)大于2.0×10^(4)t。在勘探生产实践过程中,仍需进一步持续攻关解决生排烃机制、地层条件下页岩孔隙度与含油气性测试方法与标准、富集区边界精细刻画、页岩力学性质和体积改造、提高采收率技术等难题,提高单井EUR,实现规模效益开发。

Based on the results of drilling,tests and simulation experiments,the shales of the Cretaceous Qingshankou Formation in the Gulong Sag of the Songliao Basin are discussed with respect to hydrocarbon generation evolution,shale oil occurrence,and pore/fracture evolution mechanism.Combined with a large amount of oil testing and production data,the Gulong shale oil enrichment layers are evaluated and the production behaviors and decline law are analyzed.The results are obtained in four aspects.First,the Gulong shales enter into a stage of extensive hydrocarbon expulsion when Ro is 1.0%–1.2%,with the highest hydrocarbon expulsion efficiency of 49.5%approximately.In the low–medium maturity stage,shale oil migrates from kerogen to rocks and organic pores/fractures.In the medium–high maturity stage,shale oil transforms from adsorbed state to free state.Second,the pore structure is mainly composed of clay mineral intergranular pores/fractures,dissolution pores,and organic pores.During the transformation of clay minerals,a large number of intergranular pores/fractures are formed between the minerals such as illite and illite/smectite mixed layer.A network of pores/fractures is formed by organic matter cracking.Third,free hydrocarbon content,effective porosity,total porosity,and brittle mineral content are the core indicators for evaluation of shale oil enrichment layers.Class-I layers are defined as free hydrocarbon content equal or greater than 6.0 mg/g,effective porosity equal or greater than 3.5%,total porosity equal or greater than 8.0%,and brittle mineral content equal or greater than 50%.It is believed that the favourable layers are Q2-Q3 and Q8-Q9.Fourth,the horizontal wells in the core area of the light oil zone exhibit a high cumulative production in the first year,and present a hyperbolic production decline pattern,with the decline index of 0.85–0.95,the first-year decline rate of 14.5%–26.5%,and the single-well estimated ultimate recovery(EUR)greater than 2.0×10^(4)t.In practical exploration and production,more efforts will be devoted to the clarification of hydrocarbon generation and expulsion mechanisms,accurate testing of porosity and hydrocarbon content/phase of shale under formation conditions,precise delineation of the boundary of enrichment area,relationship between mechanical properties and stimulated reservoir volume,and enhanced oil recovery,in order to improve the EUR and achieve a large-scale,efficient development of shale oil.