The Feasibility for Potassium-Based Phosphate Brines To Serve as High-Density Solid-Free Well-Completion Fluids in High-Temperature/High-Pressure Formations

Abstract

Summary Many oil and gas resources in deep–sea environments worldwide are often located in high–temperature/high–pressure (HT/HP) and low–permeability reservoirs. The reservoir–pressure coefficient usually exceeds 1.6, with formation temperature greater than 180°C. Challenges are faced for well drilling and completion in these HT/HP reservoirs. A solid–free well–completion fluid with safety density greater than 1.8 g/cm3 and excellent thermal endurance is strongly needed in the industry. Because of high cost and/or corrosion and toxicity problems, the application of available solid–free well–completion fluids such as cesium formate brines, bromine brines, and zinc brines is limited in some cases. In this paper, novel potassium–based phosphate well–completion fluids were developed. Results show that the fluid can reach the maximum density of 1.815 g/cm3 at room temperature, which makes a breakthrough on the density limit of normal potassium–based phosphate brine. The corrosion rate of N80 steel after the interaction with the target phosphate brine at a high temperature of 180°C is approximately 0.1853 mm/a, and the regained–permeability recovery of the treated sand core can reach up to 86.51%. Scanning–electron–microscope (SEM) pictures also support the corrosion–evaluation results. The phosphate brine shows favorable compatibility with the formation water. The biological toxicity–determination result reveals that it is only slightly toxic and is environmentally acceptable. In addition, phosphate brine is highly effective in inhibiting the performance of clay minerals. The cost of phosphate brine is approximately 44 to 66% less than that of conventional cesium formate, bromine brine, and zinc brine. This study suggests that the phosphate brine can serve as an alternative high–density solid–free well–completion fluid during well drilling and completion in HT/HP reservoirs.

Application of High-Density Brines in Drilling and Completion Fluids: Current Insights and Future Perspectives

“…For a normal pressure system, low-density brine completion fluids are considered and vice versa. 69 High pressure (abnormal) requires high-density brine, however, of 1.8 g/cm 3 or higher, which could pose a challenge to formulate based on available salts. The fluid must have a high density, which is typically achieved by adding salt to the fluid.…”

“…104 Bromide brine and zinc brine are known for displaying significant corrosion tendencies, despite their benefit of having high density. 105 An ideal completion fluid should exhibit a minimal corrosion rate when in contact with the steel employed in corrosion evaluation. Jia et al investigated that phosphate-based high-density brines are comparatively better in inhibiting corrosion and resulted in a low corrosion rate.…”

“…Jia et al investigated that phosphate-based high-density brines are comparatively better in inhibiting corrosion and resulted in a low corrosion rate. 105 3.1.2.7. Environmental Impact.…”

Barite-Free Muds for Drilling-in the Formations with Abnormally High Pressure

“…After running and cementing the surface casing, the drilling operator often continues to drill with the WBM unless conditions in the well require replacing it with an oil-based or synthetic-based mud. For abnormally high pressure, it is reasonable to use muds based on brine saturated with heavy salts (bromides or formates) [20][21][22].…”

Multi-Mixed Metal Hydroxide as a Strong Stratigraphic Nanoclay Inhibitor in Solid-Free Drilling Fluid

“…Its low viscosity is conducive to high-pressure injection. The stable performance of solid-free drilling fluid is easy to maintain and handle and reduces the cost of drilling fluid [ 1 ]. A solid-free system has been used in specific low-pressure and low-permeability formations since the 1980s and has been applied to some extent [ 2 , 3 ].…”