Producing-Gas/Oil-Ratio Behavior of Multifractured Horizontal Wells in Tight Oil Reservoirs

Abstract

Summary Horizontal wells with hydraulic fractures in tight oil reservoirs show producing-gas/oil-ratio (GOR) behavior that is very different from conventional, higher-permeability reservoirs. This paper explains the reasons for the observed behavior by use of reservoir simulation, with field examples from the STACK and SCOOP plays of the Anadarko Basin in central Oklahoma. A framework for interpreting observed GOR behavior in tight black-oil reservoirs is modeled after the following stages in a well's history. Some stages may not be visible because of the degree of undersaturation, flowing-bottomhole-pressure schedule, finite-conductivity fractures, and duration of the transient-flow period. Stage 1: Early GOR is constant at the initial solution GOR (Rsi) while bottomhole flowing pressure is above the bubblepoint. Stage 2: A rise in GOR as bottomhole flowing pressure declines to less than the bubblepoint. Stage 3: The transient GOR “plateau”, which is characteristic of transient linear flow. Stage 4: A continuous rise in GOR during boundary-dominated flow. Fundamental differences between linear and radial flow, which cause the dependence of GOR on flowing bottomhole pressure, are explained by use of simulation. During transient linear flow, the GOR response to changes in flowing bottomhole pressure is independent of permeability for infinite-conductivity fractures, but not for finite-conductivity fractures. Several practical observations are made. Knowing Rsi and the transient-GOR-plateau level in an area can help one interpret where a well is in its GOR history. Rate-transient-analysis (RTA) diagnostic plots are altered by rising GOR, and sometimes show an early unit slope. During boundary-dominated flow, GOR is more a function of cumulative production than of time; wells with closer fracture spacing have a faster GOR rise with time, but also recover oil more quickly. If compound linear flow develops, GOR can decline late in the well life. The Meramec and Woodford formations in STACK can be history matched without invoking a suppressed bubblepoint caused by pore-proximity effects. The critical gas saturation in the Meramec appears to be in the range of 0–5%. Technical contributions include a framework for interpreting GOR behavior over well life; the effect of changing bottomhole flowing pressure on GOR; the effect of fracture spacing, conductivity, and half-length on GOR; and the effect of GOR on RTA diagnostic plots.

Further Investigation of Effects of Injection Pressure and Imbibition Water on CO2 Huff-n-Puff Performance in Liquid-Rich Shale Reservoirs

“…The combination of horizontal drilling and multistage hydraulic fracturing technologies has made it economical to unlock oil and gas from unconventional reservoirs. − Several giant unconventional plays such as Permian Basin, Eagle Ford, and Bakken have had great success in shale oil and gas production and revolutionized the energy landscape in the United States. − However, the liquid production has a steep decline curve in all the unconventional wells, and recovery factors are estimated to be less than 10% of OOIP. , Many wells were initially produced at too high of a drawdown, resulting in acceleration of pressure-dependent permeability loss, early pressure drop below the bubble point, and preferential gas phase mobility (increasing GOR), all resulting in low recovery factors. − Therefore, effective enhanced oil recovery techniques are needed to displace oil from nanoscale shale matrix, maintain profitable oil production rates, and increase the ultimate oil recovery. ,,, Several EOR methods such as water flooding, chemical flooding, gas injection including gas flooding and gas huff-n-puff were evaluated. As the permeability and porosity in shale reservoirs are extremely low, it is difficult to conduct water and chemical flooding.…”

Greenhouse gas emissions from U.S. crude oil pipeline accidents: 1968 to 2020

“…It is imperative to calculate the GHG emissions resulting from pipeline accidents by considering the production gas-oil ratio (PGOR) and conditions whether combustion/explosion occurs. PGOR refers to the ratio of natural gas to crude oil produced from oil wells in the process of oil field exploitation 29 . It can be derived from historical production data in the U.S., as shown in Eq.…”

An Efficient and Robust Method to Predict Multifractured Horizontal Well Production in Shale Oil and Gas Reservoirs

“…Bring Equation ( 7) into Equation ( 8) to eliminate the time t; Equation (9) showing the relation of cumulative production Q and production rate q is obtained.…”

“…The research result of MFHW production performance in shale oil and gas reservoirs shows that there are mainly three flowing periods: early-stage transient flow period, linear flow period, and boundary-dominated flow period [1][2][3][4]. The linear flow period can be subdivided into transient linear flow period and compound linear flow period, and it is the most important flowing period of shale oil and gas production cycle produced by MFHW [5][6][7][8][9]. After formula manipulation of the linear flow model [10][11][12][13][14], it shows that the cumulative production Q has a linear relation to the logarithm of production rate q.…”