什邡蓬莱镇组应力剖面特征及压裂对策研究

Characteristics of Stress Profile and Fracturing Measures of Penglaizhen Formation, Shifang Gasfield

什邡气田蓬莱镇组储层致密,需通过水力压裂改造才能获得工业产能,但压后评估发现效果差别较大;由于地应力剖面特征影响着水力压裂施工所产生的裂缝产状等参数,而裂缝产状又影响压裂效果,因此,要科学、高效地开发该气藏,实施合理的水力压裂增产措施,开展地应力剖面特征研究是十分必要的。利用弹簧组合模型计算出地应力剖面,分析了其特征,确定了类型,运用PT压裂软件模拟了各种类型地应力剖面的裂缝产状、压后效果。研究发现,储层位于低应力段类型的井压裂的缝高小、裂缝长度长,改造后的效果最好,应优选该类剖面气层进行压裂改造;储层位于高应力段类型,压裂的缝高大,裂缝长度短,压裂效果差,应避免对该类型气层进行压裂。针对低应力段位于储层上部或者下部的剖面类型,应采取控制缝高和增大施工规模的措施,对低应力段位于储层下部的剖面类型,还要采取加沉式隔离剂的措施增加下部地层的阻挡作用。根据地应力剖面类型采取相应措施后,压裂效果具有较明显提高,单井产量提高20%左右。

In Shifang gasfield, commercial gas from Penglaizhen Formation can be only obtained after hydraulic fracturing due to tight reservoir. However, stress profile feature affects fracture occurrence generated in fracturing, further impacting on a fracturing effect. As a matter of fact, there is a big difference among fracturing effect. So, to carry on reasonable hydraulic fracturing stimulation and to implement a study on stress profile characteristics are very essential to effectively and scientifically develop Penglaizhen gas reservoir. In this study, the stress profile is calculated by means of a spring compound model, and its features and types are analyzed and determined. Moreover, a kind of software called PT fracturing model is applied to simulating fracture occurrence and after-fracturing effect. Results show that(1) when a reservoir is located at an interval with low stress, a best fracturing effect can be gained, i.e.,small fracture height and long fracture length. Fracturing should be implemented for this type of reservoir; and(2) on the contrary, when a reservoir is located an interval with high stress, poor fracturing effect will be come. Different measures should be adopted for the low stress interval which is located at upper and lower reservoir, for example, to control fracture height, to enlarge stimulation scale. For the stress interval located at the lower reservoir, anther measure to add submerging separant should be used to increase holdback for the lower. Consequently, the fracturing effect gains an obvious increase and the single-well yield rises by 20 %.