Water management for steam-assisted heavy oil production

Introduction

Water supply challenges

Introduction

In-situ production of heavy oil using steam-assisted methods such as SAGD requires considerable volumes of water. It can also produce large amounts of waste water that must be treated then reinjected or safely disposed of. In addition, to avoid potential contamination of nearby potable groundwater resources, it is necessary to monitor and control the flow of water within the hydrocarbon reservoir and wells. In several parts of the world, the progress and viability of heavy oil projects can be seriously impacted by water-supply issues. Similar issues can also impact shale gas, coalbed methane and conventional oil production. Oilfield technology can enhance the value of hydrogeological tools to help overcome these challenges.

Water supply challenges

SAGD operations require a lot of water. Under current available technologies, recovery of each barrel of heavy oil produced from oil sands typically requires between 2 and 4 barrels of water, most of which is usually recycled. Economic development is already placing pressure on the existing water resources of Alberta. It lies in the rain shadow of the Rocky Mountains, which causes its southern prairies to be the driest part of southern Canada. Oil sands currently account for 65% of water withdrawn from the Athabasca River, and the majority of this water never returns to the river. Canada is not alone regarding water supply challenges: US “tar sands” are primarily concentrated in Eastern Utah, which is relatively arid, so there are concerns that the development of a commercial extraction industry could have significant social and economic impacts on local communities (U.S. Bureau of Land Management).

Lack of adequate water supplies can be a “show-stopper” for economic expansion. In the  South  Saskatchewan River basin, no new surface or potable groundwater supply allocations are available from the government of Alberta for injection into oilfields, and the same is expected to apply to the northern part of the province in the near future. This means that heavy oil producers must increasingly apply innovative technologies and water management techniques to develop and maintain their own sources of water.

Protection of potable water supplies is a major issue, so the heavy oil industry is increasingly looking for deeper aquifers—often saline—as sources. Aquifer storage and recovery (ASR), although not implemented today, is another potential source of water management for the future. For example, water from the Athabasca River could be pumped into an aquifer during its spring peak flow period, and the water extracted for use during dryer months. ASR is typically 4-20 times cheaper than storing water at the surface, and requires less surface infrastructure, so could save considerable cost while providing a more environmentally sensitive solution.

Wastewater disposal challenges

Oil companies operating in the heavy oil areas of Alberta, are typically required to recycle 95% of the water produced with oil and this water is likely to require treatment before it can be reused for steam generation (Source: Environmental Challenges and Progress in Canada's Oil Sands). Excess water production is a challenge in the Faja heavy oil region in Venezuela, where Petrocedeño (formely SINCOR) produces 8.4° API gravity through about 350 horizontal wells. Inizan et al. (2008) report that 195,000 bbl of heavy viscous oil is produced each day along with 130,000 bbl of water from a large regional aquifer (Source: Water issues associated with heavy oil production). As a result, Petrocedeño is taking measures to minimize water production.

Ensuring that water or steam is injected into the right zones requires an understanding of the multiphase flow and hydrogeology of the heavy oil reservoir and also the hydrogeology of surrounding strata. This is important not only to optimize oil recovery, but also to ensure containment of contaminated water in the long term; for example ensuring that water from the hydrocarbon reservoir does not flow into a potable groundwater aquifer or river system through connected compartments. Until recently, simple 2D models with 2 or 3 layers were commonly used to characterize the hydrogeology of individual producing fields. Today, more complex models, incorporating fine details of hydrogeology—and on more regional scales—are increasingly required.

Using oilfield technology for hydrogeological characterization

Shallow wells and traditional water exploration methods are adequate for near-surface water supplies; however, to avoid potential conflict with existing groundwater users and public policy, groundwater resource evaluation for heavy oil production is being conducted at depths that extend beyond the capability of classical hydrogeological tools. In response to public and regulatory   pressure to maximize utilization of groundwater resources on a regional basis, technologies developed for the oilfield, often previously discounted by the water services industry, are proving to be of increasing value in the development of water sources for SAGD and other heavy oil developments. Oilfield reservoir characterization technologies are also applicable to ASR, where it is essential that injected water remains available for extraction, and is not lost from the aquifer.

Seismic data has been used for hydrogeological exploration and evaluation on SAGD projects. For example, seismic data acquired in Eastern Alberta for characterizing the hydrocarbon reservoir has subsequently been effectively used to map shallow features such as pre-glacial channels incised into the bedrock surface. In this case, the channels play an important role in the hydrogeological setting in the area, and needed to be recognized and defined as early as possible in the project development process.

3D seismic imaging is already widely used to characterize heavy oil reservoirs, so using the same data for hydrogeological purposes represents excellent value. Oil sands are usually relatively shallow, so the seismic reflection data generally contains high frequencies, which enables high resolution: potentially imaging layers as thin as 1 meter vertically and as small as 5 meters horizontally. Oil sands developments also normally provide large volumes of downhole data, acquired while drilling and from wireline logging. These data provide valuable information not only about the hydrocarbon reservoir, but also about surrounding strata that may provide sources of water, or act as conduits for leakage. Campbell suggests that even more effective use of seismic and logging technology can be made if there is recognition at the planning stage that the results will be used for hydrogeological characterization as well as reservoir characterization.

Several other oilfield technologies are applicable to the exploration and development of deep aquifers, such as deeper drilling than is usual for groundwater production, directional drilling, deep well completions, fracturing, slickline well services and downhole pumping technology. Advanced systems such as Petrel seismic-to-simulation software can enable seismic, petrophysical and other data to be combined to build a conceptual hydrogeological model describing aquifer characteristics on a regional basis. Software packages such as ECLIPSE are available for the simulation of multiphase flow in the hydrocarbon reservoir, providing an indication of the movement of water under proposed production and injection scenarios.

Tolerances regarding environmental sensitivities are decreasing, while costs of water supply are going up, so accurate characterization and simulation of oil reservoirs and aquifers will have increasing value in selecting sites for SAGD operations. For example, if heavy oil or bitumen is found to be in contact with fresh water aquifers, it would probably not be a good site. Conversely, if studies can show that the risk of contaminating potable groundwater is small, and that suitable water supplies are available, perhaps from a deep saline aquifer, then the site is more likely to receive planning approval.

About Ken Campbell

Ken Campbell is a senior hydrogeologist with Schlumberger Water Services, where he supports internal integrated projects and provides consulting services to various organisations in the private and public sector. His areas of technical interest include petroleum hydrogeology, waterfloods, groundwater modelling and oil sands. He began his career in hydrogeology more than 40 years ago at the Research Council of Alberta. His subsequent career path has included a wide variety of hydrogeologic projects, such as groundwater supply programs, regional mapping, mine dewatering, environmental impact studies, groundwater contamination investigations and remediation. In addition to extensive experience in various parts of Canada and the USA, Campbell has worked on projects in India, Vietnam, Oman, El Salvador, Chile, and Peru.

References:

Argonne National Laboratory (prepared for U.S. Department of Energy): “Water Issues Associated with Heavy Oil Production”

CAPP 2008: Canadian Association of Petroleum Producers: “Environmental Challenges and Progress in Canada's Oil Sands”.

Government of Alberta: “Oil Sands Facts and Statistics”.

U.S. Bureau of Land Management: “Programmatic Environmental Impact Statement (PEIS) for Oil Shale and Tar Sands resources”.