Fractured Reservoir Discrete Feature Network Technologies

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TAGS is a recovery process designed to maximize oil recovery from a thick or structurally “tall” fractured reservoir containing intermediate to high gravity crude oil. In this task, discrete fracture technologies will be applied to the yates field TAGS process study site.

• Task 4.1: Reservoir Performance Data Collection
• Task 4.2: Simulation of Fractured Reservoir Production
• Task 4.3: Technology Evaluation

Discussion:

TAGS is a recovery process designed to maximize oil recovery from a thick or structurally “tall” fractured reservoir containing intermediate to high gravity crude oil. The process relies on gas-cap inflation to maximize the vertical driving force for segregation of gas and oil while applying heat to reduce the resistance to gravity segregation. Heat provides a means of segregating hydrocarbon components by steam distilling/boiling the light components of the matrix oil into the adjacent fractures where they are highly mobile. The directional flow properties of naturally fractured reservoirs provide the means to maintain segregation of hot injected fluid from vapors evolving from the matrix blocks (matrix serves as a “semi-osmotic” membrane allowing heat to pass into it but not passing injected fluids through it). In this way injected and produced fluids are both vertically and areally segregated rather than being continuously mixed in a multi-phase horizontal displacement. The opportunity exists to operationally maximize the combined benefits of vertical, areal, and compositional segregation which is generally lost under classic steamflood operations. The TAGS recovery process relies on various forms of heat injection which preferentially target a gas cap; including steam, hot gas, and microwave or electric heating with gas assist. Heat provided by hot water or low quality steam provides less TAGS recovery benefit/ Btu.

There is no known TAGS recovery process underway; however, there have been a number of fractured reservoir steamfloods which have shown economic potential without the efficiency enhancements of a TAGS based operation. During a Yates TAGS implementation, recovery will be enhanced by four processes, 1) Ongoing gas-cap inflation, 2) Thermal stimulation of oil withdrawal from a warmer oil column, 3) Compositional enrichment of produced oil and gas in light hydrocarbons, and 4) Accelerated liquid drainage through the matrix. Analogue thermal projects generally are converting from non- productive primary depletion to steamflood operations under which well completion and operation requires dramatic change. Numerous operational problems can be avoided by applying a TAGS process rather than a steamflood operation in fractured reservoirs. TAGS production and injection operations are essentially the same as gas-cap inflation operations (extraneous gas injection is merely supplemented by injection of a condensable hot gas, steam).

Figures 2-4, 2-5 and 2-6 illustrate the implementation of TAGS at Yates Field. Figure 2- 4 shows the types of well completions at the Yates Field site. Injection wells are completed as open hole to enhance connection to natural fractures. Gravity-stable operations provide the opportunity to inject gas and produce oil from the same well. Many withdrawal completions are cased or partially cased although a significant number are completed open hole with full gas cap exposure. The TAGS process uses gravity, preferential fracture connectivity and phase behavior to segregate oil and enriched hydrocarbon gases for efficient withdrawal (Figure 2-5). Heat added to the rock column are varying oil saturations helps the oil to segregate into an efficiently-producible oil column. Figure 2-6 shows the TAGS process in a reservoir with a preferred and secondary fracture flow orientation. Heat-carrying fluid is injected at openhole completion 132 with incremental oil recovery at the deep producer (136). A second response well (126) along the preferential flow direction will benefit from both thermal viscosity reduction and improved drainage of oil and light hydrocarbon flashing in the matrix in the gas cap. The third response well (130) is not along the preferred flow direction but will respond later as heat conducts through the matrix to this location. Another type of completion in the field is a short radius horizontal drainhole. These drainholes which have logs, production and temperature surveys provided valuable data for characterizing the nearly vertical fractures in the reservoir.