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Over 13,000 active oil and gas wells and more than 740 million bbl of oil have been produced from conventional vertical wells in Utah's Uinta Basin (Fig. 1). Located within the basin, the Monument Butte area is among the top 100 oil fields in the United States. Operators with a strong presence in the Monument Butte area are also pursuing ideal target zone(s) for horizontal wells by evaluating various sections of the reservoirs and utilizing the availability of technological advances made in recent years in horizontal drilling. Determining the reservoir water source zones to curb water disposal costs and ascertaining the productivity of different segments of a well to evaluate its profitability are more important than ever considering the current economic situation. This paper will highlight the completion diagnostic results obtained from using oil-soluble and water-soluble tracers during the completion of eight conventional vertical wells in the Monument Butte area. The eight wells selected for this study are located in Sections I, II and III in Uintah County; the wells were drilled through and completed for comingled production in the Green River and Wasatch formations. Through the deployment of hydrocarbon tracers and fluid tracers, oil contribution and water production were evaluated across all zones. Between 3 and 12 hydraulic fracturing treatments were pumped into each vertical well. The fracturing treatments were designed similarly and each stage was meant to stimulate a unique target zone or formation. Moreover, for each well, each stage design had a unique set of oil-soluble and water-soluble tracers. Oil-soluble tracers were used to quantify the hydrocarbon contribution for each segment from samples taken during the course of 30 and as long as 410 days. In addition, the water-soluble tracers were used to clearly determine the water source intervals, allowing the abandonment of deeper wet zones, thus realizing a significant cost savings from not drilling and completing the bottom 800 to 1,000 ft of each future well. Finally, the unique sets of oil and water tracers were also used to evaluate the short-term and long-term productivity of each pay zone, with the intention of identifying the best formation(s) to target in horizontally drilled wells.
Over 13,000 active oil and gas wells and more than 740 million bbl of oil have been produced from conventional vertical wells in Utah's Uinta Basin (Fig. 1). Located within the basin, the Monument Butte area is among the top 100 oil fields in the United States. Operators with a strong presence in the Monument Butte area are also pursuing ideal target zone(s) for horizontal wells by evaluating various sections of the reservoirs and utilizing the availability of technological advances made in recent years in horizontal drilling. Determining the reservoir water source zones to curb water disposal costs and ascertaining the productivity of different segments of a well to evaluate its profitability are more important than ever considering the current economic situation. This paper will highlight the completion diagnostic results obtained from using oil-soluble and water-soluble tracers during the completion of eight conventional vertical wells in the Monument Butte area. The eight wells selected for this study are located in Sections I, II and III in Uintah County; the wells were drilled through and completed for comingled production in the Green River and Wasatch formations. Through the deployment of hydrocarbon tracers and fluid tracers, oil contribution and water production were evaluated across all zones. Between 3 and 12 hydraulic fracturing treatments were pumped into each vertical well. The fracturing treatments were designed similarly and each stage was meant to stimulate a unique target zone or formation. Moreover, for each well, each stage design had a unique set of oil-soluble and water-soluble tracers. Oil-soluble tracers were used to quantify the hydrocarbon contribution for each segment from samples taken during the course of 30 and as long as 410 days. In addition, the water-soluble tracers were used to clearly determine the water source intervals, allowing the abandonment of deeper wet zones, thus realizing a significant cost savings from not drilling and completing the bottom 800 to 1,000 ft of each future well. Finally, the unique sets of oil and water tracers were also used to evaluate the short-term and long-term productivity of each pay zone, with the intention of identifying the best formation(s) to target in horizontally drilled wells.
Chemical tracer is an alternative technique for hydraulic fracture diagnosis other than tiltmeter and microseismic mapping. Fracture volume is an essential parameter for stimulation optimization and production forecast. In our previous work, we proposed a simple, cost-effective method to assess the fracture volume using partitioning chemical tracer. In the hydraulic fracturing stage, a partitioning chemical tracer slug is injected along with the fracking fluid. In the created hydraulic fracture, the tracer partitions in both vapor and liquid phases and flow back in the production stage. By analyzing the tracer production data, we could estimate fracture volume and leak-off volume. This work will first investigate chemical tracer selection criteria for the purpose of fracture volume diagnosis. Tracer partition coefficient and tracer adsorption are the main considerations. Our results suggest a careful section is needed for partition coefficient, balancing the estimation accuracy and investigation area. In addition, the selected tracer should have negligible adsorption. Numerical simulation is another way to interpret tracer test. In the second part of this paper, we propose a modified Random Walk Particle Tracking (RWPT) algorithm to simulate the partitioning chemical tracer transport with multiple mobile phases. Output obtained through the RWPT is identical with analytical solution and its tracer critical breakthrough time is more accurate than the result from the finite-difference based simulations.
In horizontal-well, plug-and-perforate completions, various studies have shown that not all perforation clusters are stimulated equally. To increase perforation cluster treatment efficiency, engineers attempt to move the perforations of each stage to similarly-stressed rock. Most of these efforts have not included predictions quantifying efficiency improvements. This paper outlines a methodology for predicting improvements of perforation cluster treatment efficiency and includes a case study verifying the results of the model using pre-treatment diagnostics. In four Western Anadarko Basin wells, the operator measured mechanical rock properties using drill bit geomechanics. These properties were used to calculate the changes in minimum horizontal stress along each ~5,000-ft horizontal well. Within each treatment stage, the engineers chose perforation locations to minimize the difference in minimum horizontal stress. Using offset vertical logs and the geosteering interpretations, the engineers built a high-resolution fracture simulation model for each well. The model included the measured mechanical properties along the wellbore path. Comparing results from a geometric perforation model and the stress-balanced perforation model, the engineers predicted increased perforation cluster efficiencies between 10 and 20%. The four wells were completed using the stress-balanced perforation designs. Like all previous wells in the area, the operator performed step-down rate tests on these wells before each stimulation treatment. The step-down rate test is a common hydraulic fracturing diagnostic to quantify the number of open perforations taking treatment fluid. Compared to the operator's previous geometrically-perforated wells, the wells with the stress-balanced perforation designs showed more open perforations. A higher number of open perforations suggests a greater perforation cluster treatment efficiency. The increase in efficiency measured by the step-down rate tests was consistent with the model predictions. By understanding how stress-balancing perforation clusters will affect perforation cluster treatment efficiency, operators can optimize stimulations. The industry has not widely adopted stress-balanced perforation designs or other ‘engineered’ completion strategies. The results of ‘engineered’ completion studies have often been inconclusive, likely due to small sample sizes and reliance on production results. By combining affordable measurement of rock properties, modeled perforation cluster efficiency, and an affordable measurement of perforation efficiency, this paper provides a methodology for economically optimizing multi-stage stimulations in horizontal wells.
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