DI-74 – DISPOSAL OF OILFIELD WASTE IN UNCONSOLODATED MEDIA BY SLURRY FRACTURE INJECTION

Sponsor: Arco Exploration and Production Technology

Proposing Companies:

Terralog Technologies, Inc. and TerraTek, Inc.

BACKGROUND AND OVERVIEW

A variety of solid oil field wastes, including produced sand, tank bottoms, drill cuttings, NORM, and crude contaminated soils from old well cellars and tank farms can be economically disposed of in an environmentally acceptable manner through slurry fracture injection (SFI). Solids are mixed into slurry with fresh or produced water and injected at high pressure into suitable sand formations. The carrying fluid bleeds off rapidly, leaving behind a pod of solid waste entombed by the natural earth stresses.

The use of slurry fracture injection for disposal of oilfield wastes is expanding rapidly worldwide. Oilfield wastes are currently being disposed of by fracture injection in the North Sea, Southeast Asia, the Gulf of Mexico, Alaska, California, Alberta, and Saskatchewan. For example, in Western Canada alone, Terralog Technologies is currently managing oilfield waste injection projects disposing of more than a million barrels of slurry per year.

Inspite of the increasing application of this technology worldwide, the fundamental mechanisms of oily waste injection into unconsolidated media remain poorly understood. Several of the specific issues remaining to be addressed are as follows:

* Fracture propagation and containment:

– How does the fracture tip propagate in unconsolidated media? How is the fracturing process affected by the degree of formation consolidation (from unconsolidated to poorly consolidated)?

– What in-situ formation properties (e.g., permeability, stresses, etc.) promote fracture containment within the target interval?

– How does the change in the formation stresses during injection affect the fracturing process (causing multiple or horizontal fracturing)?

* Storage:

– Does multiple fracturing (i.e., increased storage capacity) occur with multiple injection cycles, interspersed with shut-in periods and fracture closure?

– How do the solids in the slurry invade the formation?

– How significant is the invasion zone to the overall formation storage capacity?

– What are the relations between invasion depth and the slurry solids content, injection rate and/or pressure?

Field data indicate that fracturing occurs in a complex, episodic manner, creating a process zone of varying orientation and extent. These phenomena have also been observed in limited laboratory experiments performed for Arco in unconsolidated sand blocks. Large-scale injection produces stress changes and dilation zones which appear to be influenced by variations in waste oil content and injection rate. These poorly understood geomechanical processes have direct bearing on the containment of waste in the target interval, on the ultimate waste storage capacity of target intervals, and on the optimum operating strategies required to ensure containment and maximize injectivity into a given formation.

PROJECT OBJECTIVES

The overall objectives of the proposed work are as follows:

1. Develop an improved understanding of the fundamental mechanisms associated with oily waste injection into high porosity, unconsolidated media.

2. Develop analytical techniques to evaluate formation injection capacity and fracture containment.

3. Provide the project sponsors with practical operating guidelines (injection pressures, rates, and material concentrations) for large-scale waste injection in unconsolidated media, supported with documented field data and laboratory observations.

TECHNICAL APPROACH

Terralog Technologies and TerraTek, Inc. propose to investigate the mechanics of oilfield waste injection in poorly consolidated media through a combined program of field data analysis, laboratory testing, and analytical/numerical modeling. The following approach would be taken:

1. Review, analyze, and document field observations (injection/falloff pressure behavior, stress changes, fracture orientation) from several large-scale waste injection projects. The field data to be evaluated may include those in Terralog’s archives and/or any other data provided by the project sponsors.

2. Investigate the mechanics of waste injection into unconsolidated media through a number of laboratory tests on well-instrumented, large-scale blocks (28″ x 28″ x 30″) of unconsolidated sand. These tests would be carried out under typical in-situ stress conditions in order to address the mechanisms of fracture propagation and containment, multiple fracturing, and solids invasion.

3. Compare field observations with laboratory data in order to verify the hypothesized fracture propagation and storage mechanisms.

4. Develop analytical models to assess leakoff, stress changes, and fracture propagation and containment for oily waste injection in unconsolidated media.

5. Develop operational guidelines for assessing the formation storage capacity, injection procedures for optimum storage, and fracture containment.

QUALIFICATIONS OF THE PROPOSING COMPANIES

Terralog Technologies, Inc. has been managing a number of waste injection projects in Western Canada and elsewhere. They have developed a great deal of expertise in designing and optimizing injection disposal projects, as well as field data interpretation. Since 1993, TerraTek, Inc. has been involved in a number of Joint Industry projects related to produced water disposal (PEA#23), and drill cuttings disposal (DEA#81 Phases I and II). TerraTek is currently carrying out a limited experimental project, funded by Arco, to address some of the issues related to slurry injection in unconsolidated sand. Both Terralog and TerraTek have experienced personnel in rock mechanics, analytical and numerical modeling of geomechanical systems, and field data interpretation.