Starch-Lubricant Compositions For Improved Lubricity and Fluid Loss in Water-Based Drilling Muds

Abstract

Abstract Development of water-based mud systems that approach the performance of oil-based muds is an ongoing effort. Starch-lubricant compositions were developed as environmentally safe, non-toxic, stable dispersions in water-based drilling muds. Starch-lubricant compositions were prepared by jet cooking mixtures of water, starch, and lubricant to produce aqueous starch dispersions containing suspended lubricant droplets 1–10 microns in diameter. These droplets do not separate or coalesce. The dispersions were drum dried and milled to dry, non-oily powders containing 28% lubricant by weight. These dry powders were then tested at 5 lb/barrel in laboratory-prepared lignosulfonate drilling muds. Various commercial olefins, esters and/or polybutenes were evaluated as lubricants. Standard laboratory tests indicated that starch-lubricant compositions lowered both API and HTHP fluid loss values. More importantly, coefficient of friction values were 12–25% of the untreated base mud and were similar to the average values for oil-based muds. Muds formulated with starch-lubricant compositions usually contained only 0.5% lubricant (v/v), yet performed better than a typical field mud control containing 3% lubricant (v/v). These exceptionally good results with one-sixth the amount of a typical lubricant suggest that the size and distribution of lubricant droplets achieved in these systems may enhance lubricant efficiency. Therefore, further investigation of such formulations is warranted, including a field test to evaluate the advantages of this newly-patented technology. Introduction Drilling muds have various functions, including carrying cuttings from the hole, cleaning and cooling the drill bit, reducing friction between the drillpipe and the wellbore or the casing, and maintaining the stability of the wellbore. These mud formulations should also be non-hazardous to personnel and the environment.1–3 Today, most of the world's drilling operations use water-based drilling muds, and only 5 - 10% use oil-based muds. Although oil-based muds have lower coefficient of friction values and better wellbore stabilizing characteristics, the current trend in the oil and gas drilling industry is to increase the use of water-based muds. Some of the factors influencing this trend include changing environmental regulations intended to restrict toxic and non-biodegradable materials, logistical problems in remote locations, gas solubility in oil-based fluids, advances in lubricant additives and borehole stabilizers, and the lower cost of water-based muds. Research is currently aimed at developing environmentally safe, biodegradable, non-toxic, water-based muds that will have better lubricity, improved high-temperature performance, and better hole cleaning properties. Starch-lubricant compositions were prepared by jet cooking mixtures of lubricant, water and starch4–9. Jet cooking is a technology that has been used for decades to prepare starch solutions for industrial applications and involves pumping an aqueous starch slurry through an orifice where it is mixed with steam at high pressure and temperature10. When lubricant is added, the intense turbulence and high temperature within the cooker uniformly disperses the lubricant in the aqueous starch solution as droplets approximately 1–10 microns in diameter. These droplets do not separate and coalesce, even after prolonged standing, and dispersions can also be drum dried and reduced to dry, non-oily powders. Powders can then be redispersed in water at the drilling site to produce stable aqueous dispersions that resemble the original dispersions obtained from the jet-cooker.