Abstract

A two-dimensional, single phase mathematical model of the reservoir and surface gathering system was used to evaluate the gas reserves and to determine the most profitable future field development policy. History profitable future field development policy. History matching runs with the model indicated that the performance of the Jurassic reservoir is probably performance of the Jurassic reservoir is probably influenced by limited communication with the underlying Mississippian Pekisko formation. This geologically complex situation was successfully modeled by modifying the initial reservoir description of the Jurassic-Detrital Sand. The resulting modified porosity feet (phi h) and permeability feet (kh) maps described the effective gas reserves and effective flow capacity of the reservoir.

Prediction runs were made to investigate the effects of various combinations of compressors and infill wells on field deliverability and ultimate gas recovery. Economic analyses were made for each of the most promising prediction runs. These runs were compared with the base case and with each other to determine the number and location of wells and compressors for best operating strategy.

The best development scheme consisted of five infill wells and terminal compression. The recommended strategy is currently being implemented. Initial results indicate that reservoir performance is in close agreement with the predicted behavior.

Introduction

The Paddle River Gas Field in Alberta, Canada, consists of two Units: Paddle River Gas Unit No. I operated by Canada-Cities Service, Ltd., and the North Gas Unit operated by CDC Oil and Gas, Ltd. The field has been producing from the Jurassic-Detrital formation since 1966. Production was from five wells in the Gas Unit No. 1 at an average rate of 25 MMcf/D. Data from periodic pressure surveys was available on the periodic pressure surveys was available on the producing wells; in addition, pressure data was available producing wells; in addition, pressure data was available from twelve wells completed in the formation but not produced because their deliverability was not needed produced because their deliverability was not needed to meet the gas sales contract. Plans for future development of the Unit included an increase in the daily gas production capacity to about 60 MMcf/D.

Material balance calculations using the pressure and production data indicated substantially more gas reserves than had been determined from volumetric estimates based on geological maps. There was some geological evidence suggesting that the Jurassic formation might be in limited communication with the underlying Mississippian Pekisko formation in the central and northern part of the field. The Pekisko formation contains viscous oil with a gas cap.

Development of the Gas Unit No. 1 to obtain the desired gas deliverability required a more accurate reservoir description and a method of predicting the effect on deliverability of options such as connecting the shut-in wells to the gathering system, drilling additional wells, and adding compression. A reservoir study was therefore initiated with the following objectives:

  1. define the gas reserves accurately,

  2. determine the distribution of pore volume and flow capacity in the reservoir, and

  3. forecast future gas deliverability for alternative operating methods and find the best method.

The main tool used in the study was a two-dimensional, single phase reservoir model that includes the effects of flow in both the reservoir and gathering system. The excellent pressure data available was used in history matching runs. The resulting modified porosity-feet and permeability-feet maps described the porosity-feet and permeability-feet maps described the distribution of reserves and flow capacity, including the effects of communication between the Jurassic and Pekisko formations. Using the modified reservoir Pekisko formations. Using the modified reservoir description, the model was used to evaluate the effects of different combinations of infill wells, compression, and gathering system modification on field deliverability and ultimate gas recovery.

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