Determination of Gas Well Stabilization Factors in the Hugoton Field

On the basis of a 72-hour shut-in pressure as an average reservoir pressure, the method described here can be applied satisfactorily pressure, the method described here can be applied satisfactorily to determine the stabilization factors for different wells in the Hugoton field, and in fact for wells in any tight, dry-gas, low-pressure reservoir.

Introduction

The stabilization factor can be defined as the ratio of a well's performance under pseudo-steady state conditions to the well's performance at the end of a given length of flowing time. When a gas well is drilled, it is necessary to predict the stabilized performance of each well for the orderly exploitation of gas reserves, future availabilities of gas, future gas contracting requirements and future planning of operating facilities. When a gas well is producing from a highly permeable reservoir, only a short period of time is required for steady-state conditions to be approximately established throughout the drainage area. Low permeability reservoirs exhibit "slow stabilization" and require long periods of flow and shut-in time for determination of stabilized conditions.

The conventional way to determine the stabilization factor for wells in the Hugoton fields of Kansas, Oklahoma and Texas is to shut in the well, which was previously flowing at stabilized conditions, for previously flowing at stabilized conditions, for maximum pressure buildup. The ratio of pressure buildup at the end of 72 hours compared with the maximum pressure buildup is then designated as the stabilization pressure buildup is then designated as the stabilization factor for that well. This requires that the well be shut in long enough for maximum pressure buildup, which may take a month or more.

Because there are hundreds of wells in the Hugoton fields on which it is not practical to conduct long buildup tests, a method is needed for determining stabilization factors based on information obtained from short term shut-in tests.

The objectives of this paper are (1) to present a theoretical development of a method of determining the stabilization factor from short term tests; (2) to present an application of the developed theory to field present an application of the developed theory to field data; (3) to verify its validity by comparing the results with those obtained by the conventional long duration buildup method; and (4) to determine if the stabilization time and hence the stabilization factor changes during the life of a well.

Mathematical Description of the Method

The solution for the diffusivity equation frequently used for a true infinite medium has been referred to as the point-source solution and can be expressed as a logarithmic function.

q kt Pi - Pw = -------- ln ------- + 0.809,......(1) 4 kh crw2

which may be rearranged to read

q p = ------ (lnt + ) ,...................(2) 4 kh

where

k = ln ------ + 0.809, crw2

JPT

P. 1101