Modeling Hydraulic Fracturing Using Natural Gas Foam as Fracturing Fluids

Stranded gas emission from the field production because of the limitations in the pipeline infrastructure has become one of the major contributors to the greenhouse effects. How to handle the stranded gas is a troublesome problem under the background of global “net-zero” emission efforts. On the other hand, the cost of water for hydraulic fracturing is high and water is not accessible in some areas. The idea of using stranded gas in replace of the water-based fracturing fluid can reduce the gas emission and the cost. This paper presents some novel numerical studies on the feasibility of using stranded natural gas as fracturing fluids. Differences in the fracture creating, proppant placement, and oil/gas/water flowback are compared between natural gas fracturing fluids and water-based fracturing fluids. A fully integrated equation of state compositional hydraulic fracturing and reservoir simulator is used in this paper. Public datasets for the Permian Basin rock and fluid properties and natural gas foam properties are collected to set up simulation cases. The reservoir hydrocarbon fluid and natural gas fracturing fluids phase behavior is modeled using the Peng-Robinson equation of state. The evolving of created fracture geometry, conductivity and flowback performance during the lifecycle of the well (injection, shut-in, and production) are analyzed for the gas and water fracturing fluids. Simulation results show that natural gas and foam fracturing fluids are better than water-based fracturing fluids in terms of lower breakdown pressure, lower water leakoff into the reservoir, and higher cluster efficiency. NG foams tend to create better propped fractures with shorter length and larger width, because of their high viscosity. NG foam is also found to create better stimulated rock volume (SRV) permeability, better fracturing fluid flowback with a large water usage reduction, and high natural gas consumption. The simulation results presented in this paper are helpful to the operators in reducing natural gas emission while reducing the cost of hydraulic fracturing operation.

Nigerian Stranded Gas Utilization–Investment and Risk Analysis of a Medium Scale GTL Option

Nigerian stranded gas reserves is a vast natural gas resource opportunity (with estimates exceeding 84 trillion cubic feet or 44% of current proved reserves of 190.4 Tcf) is already being monetized especially as the global environment continues to favour low carbon footprint energy sources. Natural gas utilization projects such as Liquefied Natural Gas (LNG), Compressed Natural Gas (CNG), Independent Power Projects (IPP), Gas-to-Liquid (GTL), from associated gas (AG) have taken off, however, Nigeria still struggles with low pace of stranded gas development as a result of huge capital expenditure outlays, uncertain fiscal terms as well as inadequate infrastructure, hence, stranded gas remains minimally tapped. Not only that, they exist in pockets of fields unevenly dispersed across Nigerian fields. About 70% of the onshore stranded gas are found in fields with less than 500 billion cubic feet (bcf) reserves, severely limiting gathering system optimization opportunities. In this work, GTL option is investigated as a viable utilization option. A modular medium scale GTL plant with a capacity to produce 25,000 barrels per day of premium products, is considered. GTL economics is analyzed with and without Natural Gas Liquids (NGL) extraction. The various internal and external risks associated with its development, are also explored. Without NGL extraction accruing to the GTL owner, the project becomes unattractive and never pays out within the projected timeframe of operation. With NGL extraction, project payout is 10 years, NPV@10% is $1,132.6 million and IRR is 15.4%. From the risk assessment, the capital expenditure (CAPEX) and product prices (NGL price being the most important) are major factors affecting project economic risks. Because of the huge impact of NGL extraction on GTL economics, consideration will have to be given to alternative incentives to improve profitability where this extraction opportunity is low or non-existent by fiscal authorities.