Abstract

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 decisions.

Introduction

Pressure transient analysis (PTA) has traditionally been restricted to analytic solutions that are of certain convenient form. Solutions to more complex problems have had to be approximated or are not available.

Numerical solutions based on finite difference grids have long afforded opportunities to investigate more complex problems but have been thwarted by excessive mantime investment in terms of grid and time step control generation, typically done by trial and error, to ensure a numerically accurate solution.

New research has resulted in a PTA program, based on a numerical solution, with internal algorithms to automatically generate a finite difference grid and time step controls to provide a numerically accurate solution over early, middle and late time regions used in PTA. In practical terms, petroleum engineers can now use such numerical models to discern between physical effects, such as skin effects, and complex geometries/heterogeneities that have been historically unavailable or impractical to obtain. Given the opportunity to properly isolate the physical effects, users can evaluate corrective measures that make sense rather than applying a barrage of remedies in the field in hopes of eliminating an unknown problem. The net effect is a better translation of human and monetary investment to the end objective of efficient hydrocarbon production.

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