Trilinear flows in fractured shale gas reservoir | |
| Author | Vijak Khupviwat |
| Call Number | AIT Diss no.GE-21-01 |
| Subject(s) | Shale gas reservoirs Reservoir oil pressure Petroleum engineering |
| Note | A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Geotechnical and Earth Resources Engineering with area of specialization in Geosystem Exploration and Petroleum Geoengineering |
| Publisher | Asian Institute of Technology |
| Series Statement | |
| Abstract | This dissertation comprehensively studies gas flow of multiple fractured horizontal well in shale gas reservoir. The dissertation is structured into 5 chapters as shown in table of contents. The main work and output are summarized as follows: Shale gas is an unconventional reservoir which require specialized technique to be commercially produced due to its poor reservoir quality. Multi-stage hydraulic fracturing and horizontal well is required to provide more flow path and contact area to the reservoir. One of characteristics of shale gas reservoir is multiple pore system: matrix pores, natural fractures, and hydraulic fractures. In shale matrix, pore size is very small such that law of diffusion is used to model gas transport instead of the well-known Darcy’s law. At surface of shale matrix, gas is stored as adsorbed gas which requires pressure depletion in natural fractures to desorb. In natural fracture, gas transport follows Darcy’s law. Trilinear shale gas flow model is developed in this study considering the above-mentioned effects. The model divide reservoirs in to 3 zones: (i) outer reservoir, (ii) inner reservoir, and (iii) hydraulic fracture. Gas flows from outer reservoir to inner reservoir to hydraulic fracture, and finally to wellbore. The solution is a Laplace domain of wellbore pressure and gas production rate. The proposed model is validated and show good match with production data from the Marcellus shale, U.S. The behavior of production rate can be divided into 5 flow regimes based on the log-log slope between gas production rate and time: (i) hydraulic fracture linear flow, (ii) bilinear flow, (iii) inner boundary flow, (iv) formation linear flow, and (iv) outer boundary flow. Hydraulic fracture linear flow has 0.5 log-log slope which presents the production response from hydraulic fractures. Bilinear flow has 0.25 log-log slope which present response from hydraulic fracture and inner reservoir. Inner boundary shows significantly drop in rate which occurs when the production response reach boundary between two hydraulic fractures. Formation linear flow has 0.5 log-log slope presents slow from outer reservoir. Outer boundary flow shows greatly drop in production rate which occur when the response reach outer boundary. v Sensitivity on reservoir and well parameter is performed in section 4.3. Considering the effect of adsorption, gas flow in reservoir can be divided into 3 phases: natural fracture flow, transition flow, and total system flow. At early time, all the producing gas come solely from natural fractures which is stated as natural fracture flow. After pressure in natural fractures is depleted, gas starts to desorb from matrix surface which begin the transition flow and reach the total system flow when pressure is in equilibrium. The effect of gas adsorption is shown by diffusion coefficient and adsorption coefficient. Increasing both coefficients will increase gas production rate. From field data, the early time gas production can occur as bilinear or formation linear flow. Formation linear flow (0.5 log-log slope) at early time present production from inner reservoir in high hydraulic fracture conductivity well (CFD > 40). Bilinear flow occurs for a well with dimensionless hydraulic fracture conductivity less than 40. The production rate at late time depends on the hydraulic fracture spacing, outer reservoir permeability, and distance to outer boundary. Increasing fracture spacing will delay the boundary flow regime. Decreasing outer reservoir permeability decrease gas production rate. In summary, trilinear shale gas flow model was developed in this study is used to analyze production behavior of a multiple fractured horizontal well in a shale gas reservoir. The model focuses on linear flow at early stages of production. The model utilizes information directly from directly measurement of reservoir and hydraulic fractures properties which has advantages over conventional curve fitting method. The model categorizes production rate vs. time behavior into 5 flow regimes and presents a set of analytical equations for each of them. |
| Year | 2022 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Pham, Huy Giao; |
| Examination Committee(s) | Noppadol Phien-Wej;Avirut Puttiwongrak;Huynh, Trung Luong; |
| Scholarship Donor(s) | Royal Thai Government Fellowship; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2022 |