Abstract

In situ heavy oil, oil sand pilots and conventional oil production located in unconsolidated sand reservoirs, have experienced a variety of problems related to plugging; dissolution of silica sand conditionally used as a filter pack and erosion. The erosion is subsequently followed by a massive inflow of sand into the production wells resulting in reduction of flow capacity. To alleviate some of these problems, a new metallic filter of high porosity was designed and field tested. It employed steel wool elastically compressed and sandwiched between an inner and outer high resistance mandrels. Field testing of the new filters has revealed some erosion associated problems and a laboratory program was initiated to find the optimal design criteria for reducing the erosion damage.

For the first time, the capacity of compressed metallic wool to withstand erosion was experimentally assessed. Standard sand-jet blasting equipment was calibrated and used to determine penetration time for common well-material coupons and for compressed metallic wool filters. Filters having the compression factors ranging from 5 (density = 0.153) to 30 (density = l.ll) and metallic wool depth from 6 to 19 mm were exposed to the erosion tests and results are presented graphically and analytically. It appears that increasing the wool density or filter thickness suggests an optimum value resulting in maximum filter erosion resistance.

Photomicrographs of the eroded zones are presented in order to explain some of the mechanisms involved.

Introduction

In situ recovery pilots 1 and conventional oil production located in unconsolidated sand reservoirs have experienced a variety of problems related to erosion and massive inflow of sand into production wells. As a result, considerable research was conducted at the Alberta Research Council, sponsored by Texaco Canada Resources, into new types of well completions that would alleviate solids intrusion.

To address the problems related to the dissolution of gravel packs in a high-temperature, high-pH environment and to improve flow conditions and skin-effect identified by excessive pressure drop in the wellbore region, a solids control device was developed by the Alberta Research Council and Texaco.2 The Texaco filter employed steel wool sandwiched between an inner and outer mandrel, designed to be pan of the outer well casing directly in contact with the formation (Figure 1).

Following a field testing program in Athabasca, difficulties were revealed associated with erosion of the filter by formation solids. The presence of high permeability zones in the vicinity of the production well resulted in preferentially high fluid-velocity streams.

Entrained formation solids impacting the well, tend to erode holes through the downhole filter elements as illustrated in Figures 2, 3, and 4.

As a result of these field tests, a research program was initiated in 1987 to study methods of improving the erosion resistance of the Texaco filter and well completion materials such as J55 and N8O tubing and casing steels.

The field filters constructed to date have used wool with a bulk density in the range of 0.6 g/cc (compression factor of 20) with a thickness of 3/8 inch.

This content is only available via PDF.
You can access this article if you purchase or spend a download.