Enhanced Gas Recovery Using LPG Fracturing Fluid in Tight/Shale Gas Reservoirs (Cooper Basin)
LEI, Zhongyu, NGO, Ngoc Than, Nguyen, Viet Quoc
Engineering Honours 2015
Australian School of Petroleum
University of Adelaide
Cooper basin is a major production area in Australia with over 1200 wells in total. Due to the fact that it is primarily a fluvial-lacustrine sequence containing interbedded layers of sandstones, siltstones, shale and coal, the average permeability is low and requires hydraulic fracturing to stimulate the reservoirs. In this report, unconventional reservoirs such as tight gas, shale gas reservoirs are reviewed.
Hydraulic fracturing is a process which fractures the formation in order for the reservoir to produce at an economical rate. It involves pumping fracturing fluids at high pressure into the formation. As the flow rate increases, the pressure at the bottomhole also increases. Eventually, the bottomhole pressure becomes greater than breakdown pressure and the rocks will split. In unconventional reservoirs, fracturing the formation is essential to achieve an economical production rate.
Water-based fluids are commonly used in hydraulic fracturing operations due to their availability and low cost. However, in unconventional reservoirs, applying water-based fluids are not as effective as in normal reservoirs. Since the pore size is micro, unconventional reservoirs have high capillary pressure, which leads to trapping the fluid inside the formation. With the fluid being trapped, the effective fracture half-length reduces; fluid flowback requires a longer period and a lower load of fluid recovery. The permeability is prone to damage because of formation incompatibility, for example clay swelling. Furthermore, water-based fracturing fluids also cause en ronmental problems such as post-fracturing water disposal.
Liquefied petroleum gas, or LPG, is proposed as an alternative fracturing fluid in these unconventional reservoirs. LPG compositions are made of methane, propane, butane or as a mixture of all with an addition of additives. As water is not included, the fracture half-length is not affected and therefore production rate is not hindered by this problem.
The main aim of this project is to determine the suitability of applying LPG as a fracturing fluid in Cooper Basin through investigation of hydraulic fracturing in Merrimelia-62 field. Models were developed from using softwares such as IHS Welltest, GOHFER and ECLIPSE to simulate the hydraulic fracturing system of the field to determine the fracturing characteristics and validity of the main aim of the project. The benefits of using LPG as the fracturing fluid for hydraulic fracturing treatment are increase in well productivity, higher recovery rates, reduced gas flaring, no fluid loss after fracturing, faster clean-up process, requires less pumping power. These benefits plays an important role to the petroleum industry as these could potentially reduce the total expenses for hydraulic fracturing at the cost of exposure to higher explosion risks and expenses associate with the total flow back volume of the proppant.
The project was divided into 4 phases: Data collection for model preparation, development of hydraulic fracturing model using GOHFER, development of IHS Welltest model and development of a flow simulation model using Eclipse. By developing a hydraulic fracturing model, reservoir properties such as permeability and reservoir pressure, and fracturing dimensions were determined. These reservoir properties were then validated with the IHS Welltest model. Results from GOHFER and IHS Welltest model were then used as inputs into ECLIPSE for development of a flow simulation model to determine the production profile and flow back volume for sensitivity analysis on the feasibility and applicability of LPG in the field. In addition, a literature review focusing on fracture damage and clean-up mechanism of hydraulic fracturing, types of fracturing fluids, advantages and disadvantages of applying LPG and fracturing fluid additives to gain more understanding of the effects of fracturing fluid retention and fluid clean-up and effects of applying different mixtures of fracturing fluid types with different types of fluid additives in hydraulic fracturing treatment process.
Sensitivity analysis concluded that LPG performs better in overall in comparison to other fracturing fluid considered in terms of fracture height, proppant cut-off length, gross fracture length, average proppant concentration, average fracture width and fracture conductivity. In terms of flow back capacity, LPG is indicated as the best fracturing fluid used as the amount of flow backed volume is approximate 56% of the total amount of fluid injected into the reservoir. In addition, an increase in proppant concentration allows the fracture half-length and average proppant concentration to increase significantly. Finally, having a high pumping rate for a fracturing job with LPG as fracturing fluid is not recommended.