超深层裂缝性致密储层应力敏感性研究

Study on stress sensitivity of ultra-deep fractured tight reservoir

致密砂岩储层的应力敏感性研究对指导致密油气藏开发生产意义重大。鉴于目前常规研究方法无法模拟高温、高压的真实地层环境,以及评价标准(行业标准SY/T 5358—2010)并不适用于致密岩心的实际情况,本文在模拟真实地层高温、高压条件下,采用塔里木盆地库车东部地区的致密砂岩天然岩心进行应力敏感性评价实验。通过对实验结果进行半对数化坐标处理,并采用不同函数模型进行拟合,发现强应力敏感性岩心的渗透率与有效应力的关系符合指数递减规律,相关系数均在90%以上;随着有效应力的增加,渗透率下降明显分为"先陡后缓"2段,临界压力分别为9.5 MPa和11.28 MPa,前半段体现致密砂岩裂缝渗透率的应力敏感性,后半段体现基质渗透率的应力敏感性;通过不同岩心拟合后的应力敏感性曲线的对比发现,前半段曲线越陡,岩心微裂缝越发育。分析岩心、岩石薄片、扫描电镜、全岩X射线衍射及压汞实验数据可知,高岭石含量越高,石英等刚性颗粒含量越低,微裂缝及片状喉道发育的储层往往更容易表现强应力敏感性。

The study of the stress sensitivity of tight sandstone reservoirs is of great significance to the development of tight oil and gas reservoirs. In view of the fact that the current conventional research methods can not simulate the real formation environment of high temperature and high pressure and the evaluation standard (industry standard SY/T 5358-2010) is not applicable to the actual situation of dense core, this paper uses the reservoir of Tarim basin under the conditions of simulating real formation environment of high temperature and high pressure. The tight sandstone natural core in the eastern regions is subjected to stress sensitivity evaluation experiments. Through the semi-logarithmic coordinate processing of the experimental results and fitting with different functional models, it is found that the relationship between the permeability of the strong stress-sensitive core and the effective stress is in accordance with the exponential decreasing law, and the correlation coefficient is above 90%;With the effective stress, the increase of permeability and the decrease of permeability are obviously divided into two sections:“first steep and then slow”. The critical pressures are 9.5 MPa and 11.28 MPa respectively. The first half reflects the stress sensitivity of the fracture permeability of tight sandstone, and the second half reflects the stress sensitivity of matrix permeability. The comparison of the stress-sensitive curves after fitting different cores shows that the steeper the curve in the first half, the more the micro-cracks develop. Analysis of core, rock flakes, scanning electron microscopy, full-rock X-ray diffraction and mercury intrusion experimental data show that the higher the kaolinite content, the lower the content of rigid particles such as quartz, the micro-cracks and the reservoirs developed in the flaky throat. It is easy to express strong stress sensitivity.