Abstract

The ever-increasing application of thermal methods to recover low gravity crude oil has warrantedthe review of existing sand control techniques relative to their compatibility with high temperature environments.

The advantages and limitations of a large number of materials are considered. Carrying fluids, granular pack solids, clay stabilizers, and resin-coated pack sands are discussed. Resins used for in-situ sand consolidation processes are also reviewed, and their suitability for application in a high temperature stearn environment is evaluated.

The effects of highly deviated boreholes on the placement of pressure packs are also considered. Full scale gravel pack model studies have provided valuable clues to the procedures and materials that help to create optimum pressure packs.

Introduction

Thermal methods for the recovery of heavy oils are becoming increasingly important in the overall oil production picture. It has been estimated that steam injection accounts for 92% of all present heavy oil production.1 In Canada, reserves recoverable by thermal methods have been estimated at 6.2 billion barrels from Cold Lake and Lloydminster alone. Contributions from tar sands and heavy oil sands to the total Canadian oil production are expected to increase from 15% to 35% by 19B5-1990.2

The number of cyclic steam stimulation (huff and- Puff) projects has increased rapidly since the process was discovered quite by accident in Venezuela in 1959.3 Steamfloods have also increased, but the number of in-Situ combustion {fireflood} projects seems to have remained relatively constant.4 A recent report5 on a fireflood at Lloydminster will perhaps stimulate renewed interest in this recovery technique. There are a number of publications5,7,8,9 available for those wishing to become better informed about the many variations in thermal recovery systems.

It seems that almost all formations containing tar or heavy oil are unconsolidated sands.3,5,10,11,12,13 When heat is applied to recover the oil, sand is produced into the borehole. The purpose of this paper is to discuss sand control techniques applied in wells producing low-viscosity oils, and to evaluate their applicability to thermal recovery systems.

DISCUSSION

Unconsol idated Sands

Quite simply, unconsolidated sand formations lack cementing materials to hold the sand grains together in a coherent mass. The most common natural cementing materials are silica, calcite, dolomite, and clays. These may have been absent when deposition occurred, or may have been dissolved or altered over a period of geologic time. [t has been suggested that carbon dioxide in carbonic acid is formed during the generation of hydrocarbons. Carbonic acid is considered to be the primary agent responsible for the dissolution of carbonate minerals and feldspars. The dissolution of silica occurs when the pH of the solution increases due to the consumption of hydrogen ions during the dissolution of feldspars, or by reaction between silicic acid and bicarbonate ion.14 The solubility of silica also increases with an increase in temperature.15

Quite often the producing formation contains sufficient cementing materials to hold the sand grains together, but fluids introduced into the formation during drilling, completion and production dissolve or alter the cementing- material so that the formation loses what little cohesive strength it may have.

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