New research into wellbore modeling and grid generation techniques, has made feasible pressure transient analysis (PTA) based on a numerically simulated solution. This paper first briefly reviews the development, including determination of the gridding and time step control algorithms, and then discusses some of the technical advantages offered by a numerical model as compared to standard analytic solutions. The focus of the paper is on several field case studies. The cases presented involve partial penetration and non-Darcy flow turbulence. Since general analytic solutions for these problems are not available, this paper presents new numerical solutions for these types of problems. For example, isolation of mechanical skin from partial penetration and turbulence effects, as demonstrated in this paper, is an ongoing and critical problem with respect to evaluating the need for reperforation and/or stimulation treatments.Preliminary findings from ongoing multiple phase PTA research, including modeling production below the bubble point and gas-water coning will also be presented.The results demonstrate that a simulation approach offers a revolutionary new and completely general solution to evaluating wellbore and reservoir problems that are either very difficult or not currently possible to solve analytically. Proper and practical evaluation of well tests with a numerical approach can lead directly to bottom line profit making deci-SIons.
TX 75083-3836 U.S.A., fax 01-972-952-9435.Abstract NAM in the Netherlands is currently conducting studies to redevelop the Schoonebeek oil field, onshore in the Netherlands. Steam flooding is the envisaged process.Large volumes of produced water from this field are to be re-injected in regional depleted Zechstein fractured carbonate gas fields. Estimates of injection rates and volumes are required for reservoir selection and pumping requirements. This paper demonstrates a methodology which permits injection rate and volume predictions to be made in a simple spreadsheet model based on historical measured gas production rates and volumes. The paper describes how to convert an analytical gas productivity index solution for dualporosity systems to a water injectivity index. The conversion was validated using rigorous dual-porosity simulations and sensitised to a broad range of matrix and fracture properties. It was found that injectivity in the fractured Zechstein carbonate is constrained by the effective permeability of the fracture system and is relatively insensitive to matrix permeability and fracture spacing. This behavior was verified by calculation of a dual-porosity pseudo skin factor. Partially fractured models also demonstrate that some matrix pore space which was capable of producing gas, cannot be effectively accessed by injected water volumes.The converted water injectivity index combined with other nonlinear repressurisation, relative permeability and water viscosity effects were combined with surface pump curve and wellbore head/friction calculations to construct a spreadsheet capable of predicting long term injectivity on an individual well basis. A large number of wells were screened and optimized using this practical tool.This methodology can be readily applied to other water disposal projects targeting depleted, naturally fractured or matrix only gas fields.
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