Reactive mud cake breaker fluids in long open hole horizontal wells located across high permeability sandstone reservoirs has had limited success because they often induce massive fluid losses. The fluid losses are controlled with special pills, polymers and brine or water, causing well impairment that is difficult to remove when oil-based mud (OBM) drill-in fluids (DIFs) are used. This situation has resulted in the drive for an alternative cleanup fluid system that is focused on preventing excessive fluid leak off, maximizing the OBM displacement efficiency and allowing partial dispersion of the mud cake for ease of its removal during initial well production. The two-stage spacer application is composed of a nonreactive fluid system, which includes a viscous pill with nonionic surfactants, gel pill, completion brine and a solvent.Extensive laboratory evaluation was conducted at simulated reservoir conditions to evaluate the effectiveness of the OBM displacement fluid system. The study included dynamic high-pressure/high temperature (HP/HT) filter press tests and coreflood tests in addition to wettability alteration, interfacial tension and fluid compatibility tests.The spacer fluid parameters were optimized based on wellbore fluid hydraulic simulation and laboratory test results, which indicated minimal fluid leak off and a low risk of emulsion formation damage. Three well trials were conducted in a major offshore field sandstone reservoir drilled with OBM. All three trial wells (one single and two dual laterals), which were treated, have demonstrated improvement in production performance. This paper will discuss in detail the spacer fluids optimization process, laboratory work conducted and the successful field treatments performed.
Conventional lubricant products composed of different surfactant materials are required in water-based mud for drilling highly deviated and horizontal pay zone sections due to their lubricity associated with torque reduction and better penetration rate. Drill-in fluid (DIF) filtrate-induced formation damage in low-permeability gas reservoirs as a result of water blockage and reduced relative permeability to gas can be significant in view of the high capillary pressure associated with small pore throats. Formation damage risk assessment of the drilling lubricants utilization was therefore considered critical for a low-permeability gas reservoir development project. Lubricant product evaluation experiments were designed to provide the production impairment potential measurements using Berea and Unayzah sandstone cores with a laboratory formulated DIF and base brine containing 3-4% lubricant by volume and to confirm fluid compatibility with divalent salt (CaCl2) brine. Fluid compatibility and emulsion risk was investigated using mineral oil as the representative formation hydrocarbon fluid. Core flood and dynamic filtration tests were carried out at an estimated bottom-hole temperature of 250 °F and pressure of 1,000 psi for the high-temperature reservoirs while the compatibility tests were carried out at room temperature. Filter cake removal tests were also performed by using high pressure, high-temperature filter press equipment and synthetic disks to determine filter cake removal efficiency with acid brine breaker fluid. The obtained results from the laboratory study were integrated to evaluate and rank the lubricants based on their assessed formation damage risk. The test results showed that both lubricant return permeability and compatibility tests were important in selecting the best performance lubricant. This paper discusses the experimental analysis of the formation damage potential of 12 commercially available water-based mud (WBM) lubricants. It also provides an insight into the formation damage (FD) impact of the drilling fluid lubricants on gas reservoir deliverability.
Conventional lubricant products composed of different surfactant materials are required in water-based mud for drilling highly deviated and horizontal pay zone sections due to their lubricity associated with torque reduction and better penetration rate. Drill-in fluid (DIF) filtrate-induced formation damage in low-permeability gas reservoirs as a result of water blockage and reduced relative permeability to gas can be significant in view of the high capillary pressure associated with small pore throats. Formation damage risk assessment of the drilling lubricants utilization was therefore considered critical for a low-permeability gas reservoir development project.Lubricant product evaluation experiments were designed to provide the production impairment potential measurements using Berea and Unayzah sandstone cores with a laboratory formulated DIF and base brine containing 3-4% lubricant by volume and to confirm fluid compatibility with divalent salt (CaCl 2 ) brine. Fluid compatibility and emulsion risk was investigated using mineral oil as the representative formation hydrocarbon fluid. Core flood and dynamic filtration tests were carried out at an estimated bottom-hole temperature of 250 °F and pressure of 1,000 psi for the high-temperature reservoirs while the compatibility tests were carried out at room temperature. Filter cake removal tests were also performed by using high pressure, high-temperature filter press equipment and synthetic disks to determine filter cake removal efficiency with acid brine breaker fluid.The obtained results from the laboratory study were integrated to evaluate and rank the lubricants based on their assessed formation damage risk. The test results showed that both lubricant return permeability and compatibility tests were important in selecting the best performance lubricant. This paper discusses the experimental analysis of the formation damage potential of 12 commercially available water-based mud (WBM) lubricants. It also provides an insight into the formation damage (FD) impact of the drilling fluid lubricants on gas reservoir deliverability.
Since the late 1970's, research on the efficiency and cutting life of polycrystalline diamond compact (PDC) cutters identified elevated temperature due to frictional heating as one of the primary accelerants of wear to the diamond cutting edge. Temperatures as low as 700 °C activate the back-conversion process, whereby diamond transforms into graphite, due to the presence of catalytic metal in the diamond structure. The Oil and Gas industry responded by investing years developing technologies to reduce the temperatures that PDC's experience in application via improved hydraulics for cooling, higher quality surface finishes to reduce friction, and improved thermal stability via material structure and chemical treatments. PDC cutter technology has progressed substantially in the last 30+ years, but the challenge of synthesizing a perfectly thermally stable PDC still remains unmet until now. Recently, Zhan (2018, 2020, 2021a and 2021b) first developed a new strategy to synthesize ultrastrong and catalyst-free polycrystalline diamond (CFPCD) or binderless PDC cutters with a new world record as the hardest and tough diamond material and the highest thermal stability up to 1,400°C via his invented ultra-high pressure and ultra-high temperature (UHPHT) technology, which is three to seven times higher than conventional PDC cutters used in the industry. An initial laboratory study of a new catalyst-free extreme high pressure, high temperature CFPCD material provides the first instance of a catalyst metal free polycrystalline diamond structure that actually boosts rock cutting performance above and beyond that of the current state-of-the-art PDCs. Proof of concept CFPCD specimens were evaluated against commercial, state-of-the-art non-leached (NL) and deep leached (DL) PDC cutters in the lab. Two CFPCD grades, A & B, were run through a series of tests to evaluate their potential for rock cutting and, ultimately, for use in oil & gas drilling applications. Laboratory testing was conducted on vertical borer wear tests, KIC fracture toughness tests, and thermal degradation monitoring tests. Lab results reveal a threshold that must be exceeded in the synthesis of catalyst-free CFPCDs to achieve sufficient diamond intergrowth and structural integrity to surpass the current state-of-the-art DL PDCs. CFPCD grade A wore equivalently to a commercially available NL cutter and exhibited a toughness comparable to that of commercially available DL PDC material. Grade B, synthesized at a significantly higher pressure than grade A, cut 5.7 times the distance of a commercial NL PDC for an equivalent wearscar volume, and exhibited a 160 % reduction in wear volume comparing volume of diamond worn to volume of rock cut (or G ratios) to DL PDC after cutting the equivalent of roughly 50 miles of rock. The wearscar surface of Grade B also exhibited excellent integrity with no cracking or chipping damage compared to Grade A and commercial PDC grades. This is the first documented instance of a catalyst-free PDC achieving the best wear performance and integrity (fracture toughness) than the current PDC cutters offering on the market. Thermal stability limits of PDC cutters has greatly improved in the past 20 years, but the best commercial PDC's still rely on extending leach depths with certain performance limits. For the first time in the industry, there is a PDC material than shifts this boundary without the use of catalysts and leaching technology, producing a truly differentiable PDC cutter.
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