Water availability is an issue in many parts of the world, it is important for the industry to dispose of flowback water in an environmentally, socially, and economically friendly manner. Water management in gas shale field typically takes up approximately 5% – 15% of total well costs. The quality of the flowback fluids is dependent on a variety of different attributes including quality of the initial fracture fluid and retention time within the reservoir, formation mineralogy. The main objective of this study is to assess through literature review the impact on productivity when using unconventional reservoir production water for frac operations.
Shale gas fields are generally of a black, siliceous source rock with no free water. The water present is bounded to either clay materials or in micro-pores with average matrix porosities of 1-6%. The mechanism behind the high TDS in the flowback fluid is still not very well understood; several hypotheses exist regarding the high TDS present in flow waters. These are (i) dissolution of salts, (ii) encroachment of basinal brine, (iii) mobilization of hypersaline connate water and (iv) combinations of potential hypothesis. One of the challenges for numerical modelling of unconventional systems is to fully simulate the fluid flow within the shale formation. The one-dimensional reactive transport model assumes the injection of the fracturing fluid in an open fracture. The fracturing fluid is transported through the fracture, and then in contact with the matrix, several geochemical reactions take place, then the fluid is back produced. Geochemical data and historical composition of produced water are used to determine the in-situ formation water composition.
In shale gas field, both inorganic scale (BaSO4 and FeS2) and corrosion are considered as the biggest flow assurance challenges. The simulation results indicate that formation brine salinity is very high, with a TDS above 250,000 ppm. Among the theories that might explain the high TDS in the flowback water; the encroachment of basinal brine is the more plausible. To control BaSO4 scale, it is necessary to limit the release of Ba/SO4 from the drilling mud (DM) by adjusting the formulation of the 15% HCl spearhead. By fine-tuning the concentrations of HCl/H2SO4 and citrate in the acid spearhead.
Effective treatment of the fluids offers an attractive proposition because it reduces the high cost of disposal for operators as well as the demand for fresh water. With the improvement in produced water quality, the operators were able to increase the mix ratio of treated water to fresh water. Many operators have established a goal of 100 percent recycle for their development activities; currently operators have the goal to have at least 25% of their fracturing fluid to be composed of reused water.
