More Efficient Hydraulic Fracturing SystemsCompleted

Investment:

$40k (USD) per Sponsor

Status:

Completed

Principal Investigator(s):

Value to Sponsors

Provide production and sub-surface engineering groups the guidelines to improve the efficiency of hydraulically fracturing, improving gas production rates, and at the same time reduce the environmental footprint associated with large stimulation operations.

Corporate Associates will also benefit from a more complete understanding of the role of fracturing protocols on estimates of EUR and productive reservoir volumes.

  1. In view of the fact that there has been considerable amount of effort expended by industry and academia on related topics, an essential first step is to provide an exhaustive assessment of the state of the art for stimulating shale gas reservoirs, with specific reference to
    • industry experience of fracturing fluids used for shale gas operations (including slickwater, gel [linear or cross-linked] and hybrid systems),
    • models of hydraulic fracturing (including pressure-sensitive leakoff) as applied specifically to very tight gas formations,
    • the impact of stimulation strategies on the productivity of shale gas reservoirs, and
    • the role of natural fractures in shale gas production.
  2. A detailed report on the modeling effort expended in this project as outlined above.
  3. Estimate of potential improvement in gas production rate, EUR, productive reservoir volume, hydraulic fracture fluid efficiency, and concomitant reduction in volume of fracturing fluid pumped.
  4. Guidelines for selection of optimum fracturing parameters such as fluid viscosity and pump rate.

Commercial exploitation of low mobility gas reservoirs has been improved by multi-stage hydraulic fracturing of long horizontal wells. Favorable exploitation has been correlated with large fracture surface area in contact with the shale matrix – this surface area being created by high rate and high volume injection of low viscosity water- based fluids. The environmental and economic implications of using large volumes of water (millions of gallons per well) are attracting considerable stakeholder and regulatory attention.

Our previous investigation of shale gas production has suggested that:

  • The primary (propped) fractures are the main channels for gas production.
  • The secondary (unpropped) fracture network contributes little towards gas production. It remains as a primary depository of the fracturing fluid, but this is of little benefit. Since most of the fracturing fluid enters the secondary fracture network (from which it is probably imbibed into the shale matrix), it is perhaps not surprising that only 20 to 30% of the treatment fluid is returned during well clean-up and early production.
  • Large scale slickwater fracturing is very inefficient: the volume of the productive fractures represents only a small percentage of the volume of the fluid pumped.

Our objective is to identify more efficient fracturing fluids and fracturing protocols that would use a smaller volume of fracturing fluid to achieve a greater productive fracture surface area.

We propose a new project that will develop an alternate perspective on the impact of controllable fracturing parameters on the productivity of shale reservoirs. These can include pump rate and pressure and fluid type and viscosity, for example. The investigation will use semi-analytical and numerical techniques to model fracture development, and include specifically the role played by the natural fractures and pressure-sensitive leakoff from the main fractures. The proposed methodology is similar in principle to that adopted in our earlier investigation of shale gas production characteristics. Using analytic techniques wherever possible, we seek a middle path between empirical correlations on the one hand and large-scale numerical simulations on the other.
We envisage three levels of modeling:

  1. An isolated, individual secondary fracture opening from a main primary hydraulic fracture
  2. Primary fracture development, including pressure-sensitive leakoff, to an array of secondary fractures
  3. Primary fracture development incorporating a continuous pressure-sensitive leakoff coefficient

In each of these hierarchical steps in the model development there is interplay between the fluid mechanics of flow in the primary and secondary fractures and the stress field that opposes primary and secondary fracture opening.

Results

The final objective of this analysis will be to provide guidelines for selecting fracture fluid viscosity and pump rate that will maximize primary fracture length. It is anticipated that the volume of fracture fluid used will be substantially less than that used in current slickwater fracturing operations and that the fracture fluid efficiency will be greatly enhanced (defined as the ratio of the volume of the primary fracture to the volume of fracture fluid pumped—for slickwater we estimate the efficiency at less than 5%).

The Project duration is projected to be 12 months, commencing in 2014, as sponsorship is secured.