Performance of Gravel Packs and Slotted Liners in Heavy-Oil Operations
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 132012, ’An Analysis of the Performance of Gravel Packs and Slotted Liners in Heavy Oil Operations,’ by Nosa Akhimiona, SPE, Timothy Gorham, SPE, and Ariel Auffant, Chevron, and Jonathan Harrelson, SPE, Colorado School of Mines, originally prepared for the 2010 SPE Western Regional Meeting, Anaheim, California, 27-29 May. The paper has not been peer reviewed.

As hydrocarbon prices continue to fluctuate, it is imperative for engineers to come up with optimum and cost-effective ways of managing and developing a field. This is especially true in heavy-oil operations, where the margins are very small. The full-length paper presents an analysis/evaluation of gravel packs and slotted liners in a heavy-oil field in California with the objective of comparing gravel packs and slotted liners from a production and sand-control standpoint.

Introduction

The Midway-Sunset field is a heavy-oil field in the west San Joaquin Valley, approximately 45 miles southwest of Bakersfield, California. The field was discovered in the late 1800s and has produced more than 2.7 billion bbl of oil.

The Midway-Sunset field is 20 miles long and 3 miles wide. It is the largest oil-producing field in the lower 48 states. The field was on primary production until 1963 when enhanced-oil-recovery (EOR) procedures began. The EOR procedures include continuous and cyclic steamflooding. Cyclic steam is a process that involves repetitively steaming the well, letting it soak, then producing back through the same wellbore. Steam lowers the viscosity of the oil, allowing it to flow. However, cyclic steam heats only the near-well-bore area.

Over the years, various companies have operated different parts of the field. These companies all have had different operational cultures or philosophies. For example, one company operated some part of the field, and their completion practice was to complete the wells using gravel packs. When that company was purchased by another company, they continued to use gravel-pack completions.

In 2000, Chevron stopped completing new wells with gravel packs in the Midway-Sunset field. Three years later, the use of gravel packs was stopped in the entire field. This decision was based mostly on project economics because gravel packs were more expensive and oil prices were very low, which would result in a longer time to payout. The current practice is to use slotted liners for all new completions and sidetracks because this is less expensive, and from a project-economics standpoint, it pays out faster.

One other reason for the change in the use of gravel packs has to do with the unexpected high decline in gravel-pack production over a period of time. This can be attributed to a decrease in the effective permeability of the gravel, as a result of formation fines migrating to the void spaces between the grains. This reduced effective permeability translates to reduced production rates.  

One strategy that was used to mitigate this high production decline in wells completed with a gravel pack was to sidetrack these wells using a slotted liner. Engineers believed that the production decline with a liner would not be as steep as the decline with a gravel pack. This study re-evaluates that hypothesis.