An Expert System For Analyzing Well Performance
Authors: Hutchins L.A. , Burton R.K. , MacIntosh D.J. 
Published: December 2007

A Petroleum Engineer with BP Exploration (Alaska) in Anchorage is typically responsible for 40-80 wells. This involves monitoring and optimizing well performance; identifying remedial wellwork, sidetrack and development drilling opportunities; and preparation of programs to implement the work.

Vast quantities of production and injection information are collected at Prudhoe Bay and stored in various databases. Analysis, tracking and display of this data are fundamental to every aspect of an engineer's work. Prior to development of this system, data retrieval and display was often cumbersome and time-consuming. There were few standard analysis tools available and experienced engineers had limited time to mentor new staff.

Introduction

For the purposes of this paper the suite of software that has been developed will be known as the Well Performance System. This system was developed in an attempt to retain expertise within a mobile workforce with an increasing daily workload. Use of expert analysis to highlight potential problem wells allows engineers to quickly high-grade their work, while reducing the risk that a problem may be overlooked. This consequently reduces well down-time.

An added benefit has been the development of a fast data retrieval and manipulation system, and a versatile user interface, all of which make the engineer more productive.

Well Performance System

The Well Performance System is comprised of many components which are geographically and logically distributed between Prudhoe Bay and Anchorage. These components range from simple extraction and display of data from large databases to sophisticated applications which contain varying degrees of expertise. Each has a specific set of tasks which are unique to that module. There are interactions and dependencies between modules, but most are loosely coupled. A brief description of these modules is given below.

Daily Monitoring of Well Performance. Daily average allocated production and injection rates, wellhead temperatures and pressures, choke settings, gas-lift rates and casing pressures are the basic parameters that are screened on a daily basis to ensure that wells are performing as expected. Fast visualization of this information and pre-formatted reports allow engineers to screen their wells very quickly. Potential problems (large differences since the previous day) are flagged. A rolling 90 day window of the most recent data is available graphically (Fig. 1). This module also displays recent welltest information, and on completion of a new test calculates PI (Productivity Index) and Pwf (bottom-hole flowing pressure). PI and Pwf trends may be displayed graphically for the past 3-5 years (Fig. 2).

A second module analyzes hourly average production data. The increased resolution of this data facilitates a more detailed analysis of well performance. This module analyzes recent temperature and pressure information in an attempt to identify periods when the well may have been shut-in. It also determines when the well is choked back or experiences a major fluctuation in temperature, pressure or gas-lift rate. It then attempts to determine whether the well is producing as expected following the change and whether gas-lift behavior was responsible for the change. Anomalies and potential problems are flagged to the user. A rolling 14 day window of the most recent data is available graphically.

Production Welltest Analysis. Historically, at Prudhoe Bay, only the final results from production welltests were saved in digital form, and thirty minute averages throughout the test were available on hard copy reports. Now welltest data is sampled at two minute intervals and stored in ASCII files. This enables a more thorough statistical analysis of the test data to be performed and allows a better understanding of the well stability during the test to be achieved. This in turn facilitates a better understanding of test to test variations.

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