Calculation method of wall equivalent permeability after natural fracture drilling fluid pollution

Abstract

The invention discloses a method for calculating equivalent permeability of a wall surface after natural fracture drilling fluid pollution, which comprises the following steps of: firstly, establishing a natural fracture drilling fluid pollution model, dividing grids, and setting permeability, porosity and reservoir pressure parameters according to the actual condition of a reservoir; in consideration of the relative size of the solid-phase particle size of the drilling fluid and the pore throat of the rock, the solid-phase pollution is divided into two processes of forming a mud cake on the wall surface and invading the interior of the rock to block the pore throat to cause pollution, and the influence of the slurry solid-phase pollution on the permeability of the corresponding position is calculated according to different pollution mechanisms. And calculating the grid average permeability of the polluted natural fracture wall surface by combining the mud cake permeability and the matrix permeability, namely the equivalent permeability of the wall surface polluted by the natural fracture drilling fluid. The method is reliable in principle, simple, convenient and efficient in calculation and beneficial to accurate wall equivalent permeability distribution after drilling fluid pollution, and has guiding significance on acidification design of fractured carbonate reservoirs.

Description

technical field [0001] The invention relates to the field of petroleum engineering, in particular to a method for calculating the equivalent permeability of a wall after natural fracture drilling fluid pollution in numerical calculation. Background technique [0002] Fractured carbonate gas reservoirs are the main front for current and future natural gas development in China. During the drilling process of such reservoirs, a large amount of drilling fluid will leak into the reservoir through natural fractures, blocking the oil and gas flow channels around the well. Acidizing technology is one of the most effective methods for this type of reservoir stimulation to decontaminate drilling fluid loss. [0003] Acidizing is to inject acid liquid into the formation, dissolve the solid phase of the drilling fluid, bypass the contaminated zone, remove the pollution of the drilling fluid, and restore or improve the flow capacity of the reservoir. However, in order to realize the di...

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Problems solved by technology

The drilling fluid invasion depth can be estimated based on well logging data, but the relationship between the natural fracture parameters and the solid phase invasion characteristics of the drilling fluid cannot be established

Experiments can evaluate the pollution characteristics of drilling fluid to cores and fractures, but the experimental results can be characterized on a small scale, and the application in field design is limited

Numerical simulation is the most suitable method to describe this kind of reservoir, but most of the existing studies focus on the depth of drilling fluid invasion into natural fractures, in which empirical formulas are used to describe the solid-phase mass transfer process of drilling fluid between natural fractures and rocks. There are few reports on the influence of natural fracture fluid on the grid permeability of natural fracture walls (Li Song et al., Optimization of Fractured Carbonate Reservoir Stimulation Based on Prediction of Drilling Fluid Loss and Invasion Depth. Drilling and Production Technology, 2018,41(2): 42-45), so that in the follow-up acidizing design process, the design can only be carried out based on the penetration depth of mud in natural fractures, and the drilling fluid solid phase pollution inside the rock cannot be effectively removed

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