Water Supply Optimization - Playing With a Full Deck

Project feasibility is often dependent on identifying and establishing a reliable water source. Lucien Lyness explains how subsurface regimes are often overlooked, despite offering vast naturally-occurring storage capacity and regional continuity.

Lucien Lyness

by Lucien Lyness

Principal Hydrogeologist, Calgary

17 January 2019
Water Supply Optimization - Playing With a Full Deck

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.

WATER SOURCE

The water source can still be seasonally available excess river flow.  Commonly, water can be acquired from a river by using conventional water wells placed in river gravels.  If little or no gravel is present, shallow bedrock may be a sufficiently permeable alternative.  River water acquired in this way is known as induced recharge.  The water itself experiences subsurface filtering en route to the wells such that suspended solids are removed, representing a further advantage.

Induced recharge is a technique that is used throughout the world to draw water from rivers. Obviously, favourable conditions, such as gravel deposits or permeable bedrock, must be present. If conditions are favourable, use of this technique is elegant, since intrusion into the river itself for intake construction is eliminated. Plus, acquiring river water comes with the added bonus of removing the suspended solids load by the subsurface filtering mechanism.

CONVEYANCE

Next, the water is then pumped into a deeper aquifer that is not in communication with the river.  Conceptually, injection at a location close to source (i.e., river) offsets production close to point-of-use.  The aquifer that is in between the source and point-of-use provides a natural “pipeline”.

The amount of water pumped out at point-of-use is selected to be the same as that injected at the source.  This way, the overall change in the amount of water stored in the groundwater system is zero.  The groundwater regime, as a resource in and of itself, is thereby fully preserved.

STORAGE

Sometimes a relatively large amount of water must be stored so that it is readily and immediately available to satisfy a substantial on-demand requirement (e.g., as is typically the case with multi-stage hydraulic fracturing).  Typical means of storing water to service on-demand supply requirements include:

  • on-stream storage (i.e., a surface water reservoir);
  • off-stream storage, including:
  • enhanced impoundment of a natural depression
  • purpose build/engineered pond
  • tank farm, or fabricated tank (e.g., C-ring)

Each of the above means of storing water has genuine merit, especially where a match can be found with some combination of favourable circumstances.  For example, terrain conditions may be physically suited for the construction of an on-stream reservoir or an off-stream reservoir in a landscape depression nearby.  

Conversely, the terrain may not be physically amenable or, where amenable, not sufficiently close to point-of-use.  Further, a surface reservoir typically involves a relatively large land footprint, while licensing applications can pose troublesome challenges of a regulatory and environmental impact nature.

Dedicated ponds can have a role to play, particularly where these can be placed in close proximity to point-of-use.  On the other hand, an engineered pond is more or less a permanent structure. So, as points-of-use migrate across the hydrocarbon play, additional ponds may have to be constructed, with corresponding cost increments thereby being incurred.  

Mobile storage tanks, in contrast to constructed ponds, are highly versatile in that they are portable; whereas, engineered ponds are permanently sited.  Generally, the principal limitation with mobile storage tanks is that of comparatively low storage capacity, without recourse to a potentially inordinate number of tanks.

In contrast, where geologic conditions are favourable, subsurface permeable layers can offer vast naturally-occurring storage capacity and regional continuity.

Lucien Lyness

Lucien Lyness

Principal Hydrogeologist

Mr. Lyness has over 38 years of experience in groundwater hydrology. He offers specialist services in groundwater resource evaluation and contaminant hydrogeology. Major areas of expertise include: water well design, drilling supervision, aquifer testing and installation of groundwater observation instruments; hydrogeological site assessments in environmental applications; and design and installation of groundwater remediation systems. Mr. Lyness has also prepared environmental impact assessments and provided expert groundwater testimony at public hearings to review a number of proposed industrial developments. His international experience includes field assignments in South America, South Africa, the USA, former USSR, Tibet and Middle East.