Dissolvable Rubbers Development and its Applications in Downhole Tools

Abstract

Dissolvable tools have been used more in unconventional oil and gas operations in recent years. Sealing element is one of the important parts of the dissolvable tools. The dissolvable rubbers in the market either have low strength or the dissolution rate was low. A series of high strength dissolvable rubbers with various dissolution rate have been developed by CNPC-USA to meet the industrial requirements. The mechanical properties of the dissolvable rubbers were tested at ambient and high temperatures. The dissolvable rubber coupons were soaked in water, 0.3%, 1% KCl at 80, 90 and 120 °C for various durations up to 47 days. The mass, dimensions, volume, hardness, density, and tensile properties of the samples were measured after different durations to characterize the dissolution rate. In addition, the pressure rating of dissolvable rubber sealing element was tested in water environment at 90 °C or 100 °C and in oil environment at 120 °C for 24 hours. The dissolution rate of the dissolvable rubber sealing element was tested at 90 °C or 80 °C in brine. It was found that the tensile strength of the dissolvable rubber at high temperature was in the range of 800-3000 psi and the elongation of the dissolvable rubber at high temperature was higher than 500%, which was higher than that of the most of the commercial dissolvable rubbers. For 90-120°C rated dissolvable rubbers, the dissolvable rubber coupons were disintegrated in brine at 90 °C in 5-15 days and the dissolvable rubber was completely dissolved in brine at 120°C in 4 days. The dissolvable rubber sealing elements hold 10,000 psi pressure differential at 90 °C in water and at 120 °C in oil environment for more than 24 hours. On the other hand, the dissolvable rubber sealing element were disintegrated in 90°C, 1% KCl in 7-11 days. For 80-120°C rated dissolvable rubbers, the dissolvable rubber coupons were disintegrated in brine at 80°C in 3-10 days. The dissolvable rubber sealing elements hold 8,700 psi pressure differential for 24 hours and 10,000 psi pressure differential at 100 °C for 15 minutes. On the other hand, the dissolvable rubber sealing elements were disintegrated at 80°C in 1% KCl in 3-5 days. The pressure rating properties and dissolution rate properties of the dissolvable rubber sealing elements met the field operation requirements. The dissolvable plugs with the dissolvable rubber sealing elements have been successfully used in multiple tight-oil wells and more than 15 shale gas wells fracturing operations in China. The dissolution rate of the dissolvable rubber could be controlled by adjusting the formulations. The dissolution rate of the dissolvable rubber was independent of brine concentration. CNPC-USA has developed a series of dissolvable rubbers in the temperature range from 40°C to 175°C applications to meet different operation requirements.