Abstract
Influenced by the complex sedimentary environment, a well always penetrates multiple layers with different properties, which leads to the difficulty of analyzing the production behavior for each layer. Therefore, in this paper, a semi-analytical model to evaluate the production performance of each layer in a stress-sensitive multilayer carbonated gas reservoir is proposed. The flow of fluids in layers composed of matrix, fractures, and vugs can be described by triple-porosity/single permeability model, and the other layers could be characterized by single porosity media. The stress-sensitive exponents for different layers are determined by laboratory experiments and curve fitting, which are considered in pseudo-pressure and pseudo-time factor. Laplace transformation, Duhamel convolution, Stehfest inversion algorithm are used to solve the proposed model. Through the comparison with the classical solution, and the matching with real bottom-hole pressure data, the accuracy of the presented model is verified. A synthetic case which has two layers, where the first one is tight and the second one is full of fractures and vugs, is utilized to study the effects of stress-sensitive exponents, skin factors, formation radius and permeability for these two layers on production performance. The results demonstrate that the initial well production is mainly derived from high permeable layer, which causes that with the rise of formation permeability and radius, and the decrease of stress-sensitive exponents and skin factors, in the early stage, the bottom-hole pressure and the second layer production rate will increase. While the first layer contributes a lot to the total production in the later period, the well bottom-hole pressure is more influenced by the variation of formation and well condition parameters at the later stage. Compared with the second layer, the scales of formation permeability and skin factor for first layer have significant impacts on production behaviors.
Highlights
Gaoshiti-Moxi carbonate gas reservoir is located in the Sichuan Basin and mainly developed in formation Z2dn4 (Meng et al, 2018; Zhou et al, 2016)
In this paper, we propose a semi-analytical model that considers the differences of porous characteristics and stress sensitivity for each layer in a multilayer commingled reservoir, in which some layers are naturally fractured vuggy formations represented by triple porous medium, and the others are tight formations characterized by single porous medium
A semi-analytical model is established to study the production performances in a multilayer stress-sensitive carbonate gas reservoir, in which the stress-sensitive permeability is determined with the laboratory experiments
Summary
Gaoshiti-Moxi carbonate gas reservoir is located in the Sichuan Basin and mainly developed in formation Z2dn (Meng et al, 2018; Zhou et al, 2016). Through the above reviews on the pressure transient analysis and production performance evaluation in multilayer commingled reservoirs, it can be seen that the presented mathematical models do not consider the great differences of porous media types for individual layers. In this paper, we propose a semi-analytical model that considers the differences of porous characteristics and stress sensitivity for each layer in a multilayer commingled reservoir, in which some layers are naturally fractured vuggy formations represented by triple porous medium, and the others are tight formations characterized by single porous medium. Applying the Stehfest numerical inversion proposed by Schmittroth (1960) in equations (10) and (11), the dimensionless well bottom-hole pseudo-pressure or dimensionless production rate of layer j in the real domain can be obtained. The detailed solution process for this model is similar with the method proposed by Meng et al (2018), and can be divided into five steps: (1) Calculate the cumulative production of individual layer (see Appendix 2), and determine the formation average pressure of each layer with MBE (material balance equation). (2) Compute the pseudo-time factor and dimensionless time after obtaining the values of stress-sensitive permeability, pressuredependent gas viscosity and compressibility. (3) Calculate the dimensionless well bottomhole pseudo-pressure and dimensionless production rate of individual zone. (4) Apply the Stehfest numerical inversion to calculate the above values in real space, according to equations (12) and (13), and the relationship of mw and pwf, calculate pwf and qgj, go to step (1) and repeat above steps
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
