吉木萨尔凹陷芦草沟组致密油储层岩石微观孔隙结构表征

Characterization of microscopic pore structure of tight oil reservoirs in Lucaogou Formation,Jimusaer Sag

综合利用高压压汞、恒速压汞和扫描电镜技术对吉木萨尔凹陷芦草沟组致密油储层岩石的微观孔隙结构进行研究。恒速压汞技术可以定量地区分样品的孔道和喉道,对大孔孔径测定准确,但是受限于较低的进汞压力,无法探测到较小的孔径。高压压汞技术因其较高的进汞压力可以准确地测定样品小孔隙的孔径。在共同的可测量区间内,通过插值计算方法求得两种测定技术的结合点,利用联合高压压汞与恒速压汞技术的方法计算获得了储层岩样的全尺度孔径分布曲线。结果表明:吉木萨尔凹陷芦草沟组致密油储层岩石样品的孔隙类型主要为粒间孔隙、残余孔隙及晶间微孔隙。样品的毛管压力曲线均不存在中间平缓段,孔隙结构复杂,分选性较差。计算得到的吉木萨尔凹陷芦草沟组致密油储层岩石孔径分布呈双峰态。根据LOUCKS等提出的孔分类法,样品孔径为0.07~1μm的纳米孔非常发育,中孔孔径为120~150μm,微孔不发育。高压压汞技术与恒速压汞技术具有物理模型一致性,两者的结合是一种准确求取致密砂岩储层岩石全尺度孔径分布的有效方法。

The microscopic pore structure of tight oil reservoir rocks in Lucaogou Formation was investigated using high pressure mercury intrusion(HPMI),rate-controlled mercury intrusion(RCMI),and scanning electron microscopy(SEM). RCMI can quantitatively distinguish the pore body and pore throat of the sample,and can accurately determine the pore size of the large pores. However,because of its lower mercury intrusion pressure,the RCMI cannot detect the small pores in the samples. HPMI with a higher mercury intrusion pressure can accurately determine the pore size of small pores of samples. The connected points of two techniques were obtained using interpolation method in the common measurable interval, and then the combination of HPMI and RCMI was used to obtain the overall pore size distribution of the tight oil reservoir rocks of Lucaogou Formation. The results demonstrate that the types of pores of the tight oil reservoirs in Lucaogou Formation are mainly intergranular pore,residual interparticle pores,and intercrystalline micropores. All the capillary pressure curves of these rock samples have no intermediate gentle section. The pore structure of these samples is complex,and the sorting is poor. The pore size distribution pattern of the tight oil reservoirs of Lucaogou Formation in Jimusaer Sag are bimodal. According to the pore size classification scheme proposed by LOUCKS,the nanopores with radii ranging between 0.07 and 1 μm are abundant. The radii of mesopores are around 120-150 μm,and the micropores are rare compared to nanopores and mesopores. Because HPMI and RCMI are based on the same physical procedure-mercury intrusion,the combination of these two techniques is an effective method to accurately obtain the overall pore size distribution of the tight oil reservoir rocks.