Underground carbon capture and sequestration (CCS) is a useful technique for separating this kind of greenhouse gas from atmosphere and store it under the surface of the earth. As a matter of fact, CO2 can be transferred to underground petroleum reservoirs which are initially contained oil and gas, or aquifers which are initially saturated with water. This kind of CCS takes place using an injection well which is drilled from surface to the target underground bedrocks. A shale gas reservoir (SGR) is a type of petroleum gas reservoir in which natural gas is stored in ultra-tight pores of the shale rock. In this study, a flow modeling analysis in SGR with a multi-stage fractured horizontal well (MSFHW) is conducted using numerical simulation. In this shale layer, a horizontal well is drilled and several transverse hydraulic fractures, for increasing the flow efficiency between the well and porous medium, are created. The studied SGR – a depleted reservoir acting as a macroscopic sustainable material for the CCS – is initially saturated with methane gas, and carbon dioxide is required to be injected for the storage. The most outstanding results of this study is about sensitivity analyses for SGR permeability with different conditions of gas adsorption and stress-dependent permeability which are from important features of SGRs. The results show a minor reduction in cumulative gas injection due to the effect of stress-dependent permeability in all measures for reservoir permeabilities. Furthermore, gas sorption shows a considerable positive correlation with CO2 storage response in high-permeability SGR and a minor increasing effect on SGRs with lower permeability values.

The application of multi-stage fractured horizontal well (MSFHW) due to its costly operation necessitates optimization of associated fracture parameters to ensure its economic success. In comparison to significant number of studies dedicated to use of MSFHWs for shale gas reservoirs, there are only few researches available for oil systems. This study explores the optimum criteria for a number of important fracture parameters in low-permeability heavy-oil systems. For this purpose, a response surface methodology (RSM) was employed to examine the simultaneous effect of four fracture parameters, including the number of fracture stages, fracture length, fracture width and fracture conductivity, on well productivity. The evaluations were conducted on two homogeneous and heterogeneous permeability systems. The optimization of fracture parameters was also performed on an economic basis by utilizing the net present value (NPV) concept. Useful charts were also generated providing practical insights into the individual and combinational effects of fracture parameters on well performance. The results from this study demonstrated that the fracture conductivity and the number of fracture stages were, respectively, the first two important parameters controlling the well productivity for rock systems with higher permeability. However, when rock texture became tighter, the number, and to a lesser extent the length, of fractures exhibited more evident role on production improvement, especially in the case of heterogeneous reservoirs. The results also underlined the significance of economic considerations, in particular, when determining the optimum fracture length and number of fracture stages.

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Wastewater injection into oil and gas fields is implemented for various purposes via injection wells. Disposing of wastewater, which is mostly waste saltwater produced with hydrocarbons in oil and gas fields, into underground petroleum reservoirs are usually tied with environmental purposes. Injection of wastewater into geologic strata may encompass different applications: hazardous or non-hazardous wastewater disposal, enhanced recovery from petroleum reservoirs or merely wastewater storage. Aside from the purpose of wastewater injection, modeling of wastewater flow in porous media of underground rock strata can be challenging in different petroleum reservoirs and wells. In this study, a tight gas reservoir (TGR)—as a large-scale sustainable material to store wastewater—is considered to be studied for water disposal via a multistage fractured horizontal well (MSFHW) by numerical simulation. Host rock layer is considered to be initially saturated with low-pressure methane gas and water injection has to be performed through the hydraulic fractures of the MSFHW into the rock pore volume. Injection is performed under constant bottomhole flowing pressure and several sensitivity analyses are investigated to outline important rock characteristics in TGRs affecting performance of wastewater injection into them.