一种裂缝流体因子的提出及应用

为了解决各向异性下的流体识别问题,将纵波各向异性裂缝预测以及Russell的流体因子融合到直角坐标系中,提出了一种能够同时检测裂缝发育情况以及流体性质的新的裂缝流体因子(Factor of Fluid-filled Fracture,FFF),并通过一组岩性参数检验了裂缝流体因子在裂缝预测及流体识别中的有效性.在理论研究的基础上,选取松辽盆地某地区的火成岩裂缝及流体识别研究为应用实例.通过与测井流体及裂缝信息的对比验证,裂缝流体因子能够较为准确地预测研究区裂缝和流体的分布情况,且裂缝流体因子在单井上的计算结果与单井含气饱和度吻合度较高.此外,根据实际应用效果,指出裂缝流体因子在应用中的局限性:裂缝流体因子在平面成图时受地层厚度影响较大,且无法预测裂缝方向.

A new factor of fluid-filled fractures and its application

Fracture and fluid property are two important factors for oil and gas prospecting. However,the fluid identification factors proposed by previous studies focus on the fluid identification based on isotropic assumption. Little work is concerned with fluid prediction and recognition of fracture fluid associated with anisotropic media. This study attempts to put forward a new parameter which can characterize fracture and fluid simultaneously,and presents its application in practical research.From geological origins,fracture and fluid are closely related. The situation of fracture development (whether or not) and the fluid properties (water or gas) is similar to the four quadrants in rectangular coordinate system,so both the fracture identification and fluid identification items can be constructed using a rectangular coordinate system. Firstly,the fluid factor of Russell is adjusted to the fluid identification item Fluid:cosθ so that the result of adjusted expression is positive when formation contains gas,or negative when formation contains water. Secondly,considering that fracture is sensitive to the P-wave impedance azimuthal anisotropy,and the value of this item is expected to decrease with increasing fracture density, the maximum and minimum of P-wave impedances are introduced to construct the fracture identification item Fracture:sinθ. Therefore,a same parameter angle θ is combined with the two above-mentioned items, which is the expected anisotropy fluid factor. Now that this factor is determined by both fracture and fluid,it is named Factor of Fluid-filled Fracture,FFF for short. In addition,through numerical calculation with a group of representative lithological parameters based on the highly porous unconsolidated sandstone model proposed by Dvorikin,the validity of the FFF in both fracture prediction and fluid identification is verified.On the basis of theoretical research,fracture and fluid identification of igneous rock in a certain area of the Songliao basin is taken as an application example. With the process of velocity analysis, pre-stack time migration and pre-stack AVO simultaneous inversion,P-wave impedance and S-wave impedance under isotropic condition, the maximum and minimum of P-wave impedances in different azimuths are obtained. By substituting the data above into the expression of FFF,the FFF volume is determined. Comparing the fracture and fluid information in two wells with the predicted results shows a good consistence. In addition,the predicted result is consistent with the gas saturation curve in a well B. So the effectiveness of the new parameter is proved.Based on the adjustment to fluid factor Russell and P-wave impedance azimuthal anisotropy, a new parameter named FFF is proposed,and its effectiveness is proved with both numerical calculation and practical application. Its technical advantages are as follows: (1) FFF can describe the distribution of fracture and fluid accurately. (2) For different ranges of FFF,fluid saturation can be characterized so that the favorable target can be identified much more conveniently. (3) The minimum and maximum of FFF respectively represent gas-bearing fracture zones and gas zones without fracture,which is intuitive for researchers to understand the characteristics of fracture and gas-bearing properties with the FFF map.