Integrated Digital Automation System for Production Optimization in the North San Juan Basin
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 106952, "Successful Application of Integrated Digital Automation System for Production Optimization in the North San Juan Basin," by Peter O. Oyewole, SPE, Michael D. Scull, and Mark S. Downey, BP plc and John B. Herring, SPE, Pure Automation, prepared for the 2007 SPE Digital Energy Conference and Exhibition, Houston, 11–12 April.

An integrated digital automation system was used to optimize tubing-flow-control and plunger-lift installations in the north San Juan basin. The intelligent closed-looped automation system increased gas production, improved equipment reliability, and provided an efficient and inexpensive deliquification method with an almost exclusively remote-controlled operation.

Introduction

Gas-well production tends to decrease over time as a result of depleting reservoir pressure. The liquids associated with the produced gas accumulate in the wellbore. The liquid column creates hydrostatic backpressure on the reservoir, which further reduces the gas flow rate. A minimum gas-flow rate is required to lift the entrained liquid droplets to the surface at a specific wellhead pressure. Several artificial-lift and dewatering methods are available to lift liquid from the bottom of the well to the surface; one is plunger lift. In some marginal gas wells, anticipated production would not justify installing artificial-lift systems such as a sucker-rod pump to dewater wells. In some applications, plunger lift is an economical choice. Plunger lift is an intermittent form of artificial lift that uses the reservoir energy to lift liquids out of the wellbore. Plunger lift has benefited from improved digital technology. The entire system can be completely monitored and optimized.

Unlike conventional natural-gas reservoirs in which gas production rates tend to be greatest at the onset, then steadily decline over the life of the well, coalbed methane produced in the north San Juan basin progressively increases to a maximum flow rate several days or years after first production. It is a challenge to match and optimize tubing and casing sizes with the ever-changing production rate. Applying optimized tubing-flow control helps to mitigate these challenges.

Integrated Digital Automation

Input/output (I/O) abstraction is the function that defines the connection between physical I/O and the applications or process I/O, or between a calculated variable and a consuming program. An example of I/O abstraction would be to assign an analog input as casing pressure. The programmer could assign the physical I/O to the casing pressure at design time so that "Analog X" is always casing pressure. In an abstracted scheme, the analog input is assigned to the casing-pressure variable at run time so that, if needed, the physical input can be assigned to another process variable if the particular installation did not have a casing pressure.

An example of a calculated value abstracted and consumed by a program is a critical-flow-rate value placed in a common index or array, and then, by use of mapping, that value is called into a subroutine program-organization unit and used to control a plunger process.