Date of Award
Doctor of Philosophy (PhD)
Horizontal well drilling and multi-stage hydraulic fracturing are two key techniques for the development of unconventional reservoir. However, the production from tight formation is associate with fast depletion of reservoir. When oil price is low, drilling new horizontal wells is not profitable. Creating secondary fractures from existing hydraulic fractured wells, i.e., refracture is an alternative method to increase stimulated reservoir volume (SRV) and gain additional production from existing hydraulic fractured wells. To optimize refracturing well selection and operation, it’s of economic importance to acquire knowledge from initial hydraulic fracturing operation, production history, and refracturing design perspectives. This initiated the idea of this research to develop an integrated hydraulic fracturing, production, and refracturing model.
This research work mainly comprises of three sections. In the first section, hydraulic fracturing models were built using XSite software, a lattice-based simulator, to analyze the effect of changing rock properties and in-situ stresses on fracture propagation in a layered reservoir. The challenge was to quantify degree of fracture containment using the hydraulic fracturing simulator. To overcome this fracture aperture contours were obtained to quantify fracture containment with two proposed penetration parameters. The modeling results suggest that brittle rocks favor vertical migration of hydraulic fracture, while increasing minimum horizontal stress tends to inhibit vertical growth of hydraulic fracture and lead to containment at layer interface.
In the Second part of this study, an innovative integrated multi-stage hydraulic fracturing and production model was built for a shale gas reservoir. The challenge was to utilize distributed fracture data presented from the lattice-based hydraulic fracturing simulator for history matching in the reservoir simulator. To identify fracture geometry, a moving tip clustering and linear regression clustering algorithms were developed to discretize distributed fracture data points using multiple crack segments. The former algorithm is prone to capture fracture with microcracks that contribute to SRV, thus contributing to higher simulated production. The latter algorithm mainly captures the major fracture path without consideration of microcracks. The modeling results also suggest that gas slippage, matrix shrinkage, and fracture closure play important roles in shale gas production.
In the third section, an innovative hydraulic fracturing, production, refracturing, and post-refracturing production model was developed. The challenge in this part was to simulate refracture propagation based on existing fracture geometry and pore pressure distribution with higher accuracy and efficiency. A model was built by simulating the fracture and refracture propagation in XSite and modeling reservoir depletion and post refracturing reservoir depletion in the continuum mechanism based simulator. The results suggest the propagation of refractures is driven by proppant and depletion induced stress shadow and contributes to larger SRV and higher hydrocarbon production.
The proposed algorithms and integrated models can potentially be applied in the field for better refracturing design to enhance ultimate recovery of oil and gas.
Wan, Xincheng, "Coupled Simulation Of Hydraulic Fracturing, Production, And Refracturing For Unconventional Reservoirs" (2020). Theses and Dissertations. 3127.