THE MISSING CARD
Water is often a vital ingredient in many industrial operations. Examples include the need for relatively large volumes of water on-demand to service multi-stage hydraulic fracturing completions, through to more continuous supplies for pressure maintenance of oilfield reservoirs. Establishing a reliable source of water can therefore be of paramount importance in respect to project feasibility.
Financially viable use of this essential resource -development commodity requires that its sourcing, conveyance, and storage challenges each be met in a cost-effective manner. In turn, all technically feasible permutations in respect to the source, transmission, and storage continuum as supply chain components need to be taken into account so that a financially optimum and workable combination can be identified. A regime that can offer one or more of these components, but is commonly overlooked because it is out -of -sight, -out -of -mind, is the subsurface environment.
Yes, an entirely ground surface-based permutation may be best suited for some applications. After all, rivers can contain substantial volumes of excess water seasonally. By the same token, what if the preferred river (source) is periodically too low? What if it is too distant from the operation? The subsurface regime can provide an already existing conveyance means between river and point-of-use, as well as storage for excess river flows.
TYPICAL WATER SUPPLY NEEDS IN SERVICING OILFIELD OPERATIONS
Common conventional and unconventional oilfield operations for which a secure water supply is integral to hydrocarbon extraction include:
- injection of water to maintain reservoir pressure such that oil production is enhanced;
- stream generation for in-situ thermal recovery of bitumen from oil sand;
- process water for the separation of oil from surface-mined oil sand;
- water for multi-stage hydraulic fracturing, for fracture generation, and as a carrier fluid for proppant and blended chemicals.
Obviously, water is inherently essential to these hydrocarbon extraction activities. At the same time, in terms of both financial and technical feasibility, where can it reliably come from, how will it be transported to where it is needed, and by which means can it be stored until required?
OPTIONS FOR ESTABLISHING A COST-EFFECTIVE WATER-SUPPLY CHAIN
In many circumstances, the best option is to source a water supply from a river, creek, or lake. River systems have a particular appeal because they can contain large seasonal flows of excess water. Licensing can be relatively straight forward when flows are high. This contrasts with seasonally low flows when potential for impact to aquatic ecosystems becomes more pronounced. In turn, it can be comparatively difficult or impossible to obtain a licence.
Therefore, a commonly used and uncomplicated way of establishing a secure water supply is to simply draw it from a river and convey it to point-of-use by means of a pipeline. After all, countless municipal supplies and industrial operations are successfully serviced in this way worldwide. The track record is compelling! Why tinker with success? Indeed, as the saying goes, “if it ain’t broke, don’t fix it!”
However, if upon consideration, the above simple scenario were to break down, owing to possible burdensome financial and/or technical detractions, other options may have to be considered. For example, the river may be too far away, posing a financially onerous length of pipeline. Land access challenges for pipeline route and/or a traverse across difficult terrain could apply. A possible alternative is to harness the subsurface or geologic regime.
Naturally occurring subsurface reservoirs, or aquifers, are commonly present and continuous at a regional scale. An aquifer’s storage capability, especially when combined with its widespread footprint, provides a potential opportunity for storing a proportionately large amount of water. The widespread footprint also provides a natural conveyance pathway from point- of- source-and-injection to point-of-use.
Coupled injection and retrieval of water to and from the subsurface is a mature technique known as aquifer storage and recovery (ASR). ASR can be tailored in various ways to serve a particular purpose. In its most obvious form, water is injected at time of excess availability, followed by its recovery in times of need. A further classic application is a combination of coastal injection and inland production to prevent induced seawater incursion into coastal aquifers.