松辽盆地徐深气田D区块营城组火山岩构造裂缝与地应力特征

Structural fractures and geostress in volcanic rocks of Yingcheng Formation,D block, Xushen Gasfield, Songliao Basin

火山岩油气藏储层具有致密性和非均质性,天然裂缝的特征及发育程度对油气藏的开发具有十分重要的影响。通过岩心描述、黏滞剩磁定向综合描述等方法研究松辽盆地北部徐深气田D区块白垩系下统营城组火山岩天然裂缝的发育特征及优势方向,应用电阻率成像测井、横波各向异性测井方法解释了该区最大水平主应力方向,采用Newberry模型计算研究区的最小主应力,基于双井径分析计算最大主应力,明确该区水平井部署的轨迹方向,为储层压裂提供依据。结果表明:①该区构造裂缝具有多期次、多方向、多组系特征,以中—小缝为主,裂缝优势方向为北西向和北东向共轭发育;②研究区最大水平主应力方向为近东西向,最大和最小主应力值分别为86.0～91.0 MPa、69.0～75.0 MPa,且二者的平面分布具有一定的相似性,总体以工区南部主应力值较高。结论认为:水平井部署的轨迹方向应为SN方向,储层压裂改造过程中施工压力应大于86.0 MPa,且工区以南部还应适当增加施工压力,以达到破裂造缝目的。

Most volcanic-rock reservoirs are tight and heterogeneous. Both feature and development of natural fractures play an important role in their exploitation. So, the development characteristics and predominant direction of natural fractures in volcanic rocks of Lower Cretaceous Yingcheng Formation, D block, Xushen gasfield, northern Songliao Basin, were at first studied by means of core and viscous remanence orientation description. Then, the direction of maximum horizontal principal stress was interpreted via using resistivity and S-wave anisotropy logging. Finally, the minimum principal stress was calculated by Newberry model, whereas the maximum one calculated by bi-diameter analysis. Thus, the trajectory direction of deployed horizontal wells was made clear to provide a basis for next fracturing. Results show that, in this area,(1) most structural fractures with medium to small in size are characterized by multi-stage, multi-direction and multi-formation, along with NW- and NE-trending conjugate development in the predominant direction;and (2) the maximum horizontal principal stress is nearly east-west-trending. The maximum and minimum principal stresses range in 86.0-91.0 MPa and 69.0-75.0 MPa, respectively, and are similar in areal distribution. In general, the principal stress is higher in southern area. It's recommended to set the trajectory direction of deployed horizontal well at SN, to keep construction pressure during fracturing higher than 86.0 MPa, and to increase this pressure appropriately in southern area so as to achieve an aim to induce fractures.