Method of Predicting the Initial Deliverability Of Shallow Gas Wells In Southeastern Alberta
Authors: Lawrence T.M. , Dzurman P.J. 
Published: March 2010

Increasing emphasis is being placed on the development of the large natural gas reserves associated with the Milk River, Medicine Hat and Second White Specks formations in southeastern Alberta.

Due to the low formation permeability encountered in these formations. short-term production test data often indicate a productive capability which is unrealistic when compared to the long-term performance of the well. This presents a difficult problem in designing the optimum gathering system and compression requirements.

The purpose of this paper is to show how data from a properly conducted single-point production test of reasonably short duration can be used to predict the initial deliverability of a well completed in one of these formations and serve as a guide when designing a system for the development of shallow gas reserves.

INTRODUCTION

THE PRIMARY OBJECTIVE of any gas well test is to obtain sufficient information reflecting the well"s performance under varying conditions of flow in order to project future deliverability. This type of projection is necessary when preparing field development programs and designing gathering and compression facilities.

Proper design of production facilities is important when considering the development of gas reserves associated with the Milk River, Medicine Hat and Second White Spects formations in southeastern Alberta. A low-deliverability shallow gas development is characterized by high well density and low pressure. Consequently, the gathering system and compression requirements usually absorb half the total development cost. Due to the low formation permeability associated with these shallow gas zones, initial flow rates rapidly decline to values substantially lower than those indicated from short-term production tests. This can lead to an over-design of production facilities and hence reduce the economic feasibility of the project.

The method described herein will show how existing techniques of flow test analysis may be used to aid the operator in predicting the initial deliverability of a well completed in one of these formations and serve as a guide when designing a system for the development of shallow gas reserves. It will also be shown how this method may be used to determine the optimum flow time required when testing the wells.

Method of Testing The modified isochronal back- pressure test is generally accepted as a reasonable method to use when evaluating gas well performance. However, when applied to the shallow, low-permeability zones of concern here, there are two major drawbacks. First, the bulk formation is not investigated within the short multi-point flow periods, but rather within a region close to the wellbore where flow characteristics are controlled primarily by the fracture system present. Second, as pointed out by Schopp(1), the extended flow period necessary: to reflect stabilization is not justified in these formations, where flow times of up to a "year or more could be required.

It is recommended that a single-point production test be conducted on the well, allowing flow rate and pressure to decline with time. The well is flowed through a critical flow prover with a constant orifice size and the flowing pressures are recorded throughout the test.