Forward Numerical Simulation Of Dual－laterolog In Shale Fractured Formation

Almost all of oil fields in the world have entered the high water cut period, and the mothball oil and gas resources are insufficient, therefore it is necessary to explore and develop unconventional reservoir, shale fractured reservoir is one of reservoir types which have a great future. It is possible to get industrial commodity of oil and gas if fracture lie in mudstone. Therefore, it is very meaningful to research shale fracture reservoir.Dual-laterolog (DLL) was used to determine fracture porosity in carbonate reservoir and to identify carbonate fractured zone, while there is little research on DLL applying in shale fractured formation, therefore the main purpose of this paper is to give some forward simulation of shale fractured formation and find log response of this kind of formation. Based on the theory of electric field of DLL tool and Laplace Equation (harmonic equation ) which satisfied by electric potential. 2-dimensional symmetric problem was taken into account on the basis of variational principle in cylindrical coordination, as a result, a large linear finite elemental equation was got. And then isoelectric surface treatment of every trode which is composition of DLL tool was handled, and also the potential solving problem is simplified by applying 1-dimensional compressed storage method, electric potential in formation and borehole, and the apparent resistivity(Ra) of DLL, would be solved out from the handled linear equations.In forward simulation, DLL electrode coefficient(value K) is a crucial factor, to determine value K accurately is very important both for logging well site and for numerical simulation of DLL. It is from electrical model of homogeneous formation one quarter plane that the response and the electrode coefficients of LLs(shallow laterolog) and LLd(deep laterolog) were achieved. The DLL problems can be decomposed three electrical fields to solve, this made it possible to solve these two problems simultaneously. The result is to be in agreement with the given value K and the corresponding conference. On the basis of this, the Tightness of calculation method is proved, and using the same method to simulate shale fractured formation.For the rotary symmetry and unlimited invasion shale fractured formation, when the electrode was lifted from bottom of borehole to the earth surface, based on the mesh generation of right angle triangle element, according to elementary resistivity weighted average formula. The conductivity matrix is achieved in fractured zone, and subsequently the potential of every nod and apparent resitivity of DLL are gotten. The influence of width, porosity, number of fracture and mud filtration resistivity on result of forward simulation result was analyzed. For existing single fracture only, fracture can be identified from the forward simulation apparent resistivity log if the fracture width is equal or greater than 0.02 meter , for numerous fractures, the more fracture, the more greater apparent resistivity varied. When mud filtration resistivity is less than shale resistivity, with increasing of fracture width and porosity, the difference of Ra and shale resistivity has a trend to increase, but the comparative difference is very small. While in high-resistivity mud, there would be greater difference. Therefore the result is very interesting, and also, with the increasing of fracture width and porosity, Ra has a trend to increase rapidly. So under this paper's hypothesis, fracture is identified easily using high-resistivity than using low one. If fracture porosity is 2%, it was derived from the simulation result that using high-resistivity mud(500 Q -m) can identify shale fractured formation which includes 750 fractures or more. Besides, some forward simulation was done for vertical fracture, the conclusion has the same trendas radical fracture. But in this case, there is difference of apparent resistivity of deep laterolog and the shallow counterpart. This was caused by different investigation depth of two methods. The shallow laterolog can't detect...