Unconventional Shale Oil and Gas-Condensate Reservoir Production, Impact of Rock, Fluid, and Hydraulic Fractures

Abstract

Development of unconventional oil and gas reservoirs, particularly the shale gas, gas-condensate, and shale oil, has gained tremendous momentum in recent years. Energy companies aggressively are adding unconventional hydrocarbon resources to their portfolios. The unconventional resources usually refer to ultra low permeability reservoirs that cannot be produced at economic rates or volumes without stimulation of near well-bore regions. New technologies of horizontal well coupled with staged hydraulic fracturing have made the development of these reservoirs an economic reality. But often, the initial attractive production rates decline fast and thus making them economically marginal and sometimes operationally unattractive. In order to efficiently produce these reservoirs, it is important to understand the flow mechanism and the controlling rock and fluid parameters that significantly impact the long term production performance of these resources.We have conducted detailed reservoir simulation studies to investigate the impact of rock and fluid properties and the drainage area of hydraulically fractured wells in a standard development pattern. The simulation of horizontal wells with 14-stage hydraulic fractures was conducted in a shale reservoir containing a wide spectrum of rock and fluid types, dry gas to gas-condensate, and oil. An extensive compositional reservoir simulation was conducted using both radial grid and sector model. Short term production data from several horizontal wells and long term production data from one vertical well were used for history matching and model calibration. A number of cases have been run with a wide range of fracture, matrix and fluid properties considering condensate banking, fracture patterns, pore volume compressibility, and relative permeability. The results showed• Cumulative oil production is sensitive to fluid properties, particularly to the GOR • Severe drop in productivity is observed due to matrix and fracture compaction and condensate banking • The drainage area and the contact area of the fractures with the reservoir are often limited in spite of extensive hydraulic fractures • Performance is also found to be sensitive to fracture permeability and matrix relative permeability • Fracture interference is limited and may occur in the late life of the reservoir

A Simple Physics-Based Model Predicts Oil Production from Thousands of Horizontal Wells in Shales

“…Orangi et al (2011) for GOR=1000 oil e Solution gas-oil ratio d p b =∼3250 psi reported for a GOR=1000 scf/stb oil in Figure 2 in Orangi et al (2011) span the bottom-hole area of 10,500 acres.…”

Factors controlling production in hydraulically fractured low permeability oil reservoirs

“…The oil production is about double in ten years when the rock compressibility is 25 times higher as shown in Figure 6(b). These trends were also observed by Orangi et al (2011). Lower compressibility rocks do not permit the structure to deform; on the other hand, higher compressible rock sustains the pressure of reservoir by squeezing the rock and reducing the pore space for overburden pressure when the pressure in the pore is reduced in course of production.…”

“…Fracture spacing affects the performance of gas-oil gravity drainage largely when the ratio of fracture spacing and fracture height is larger than 0.3 (Clemens and Wit, 2001). Oil production increases with increase in fracture permeability up to 10,000 mD and with increase in the fracture -matrix surface contact area (Orangi et al, 2011).…”

Coupled Geomechanics and Fluid Flow Model for Production Optimization in Naturally Fractured Shale Reservoirs

“…Gas and oil components were sourced from available mudlogs and missing data points were filled in with synthetic Eagle Ford black oil properties (Orangi et al, 2011) matching with the provided oil gravity (41 °API) and gasoil ratio (1,000 scf/stb) data. The Peng-Robinson Equation of State was used to predict the phase equilibrium compositions of the oil and gas phases as defined by:…”