Reduced Environmental Impact and Improved Drilling Performance with Water-Based Muds Containing Glycols

Abstract

Introduction Concern over the environmental impact of drilling operations - in particular the disposal of whole mud and contaminated cuttings - is leading to a major reappraisal of acceptable mud types and the way in which they are used. Strict control over the use and discharge of fluids is exercised in, for example, the USA, the North Sea, the Adriatic and the CIS. Government agencies in almost every area of the world are conscious of the potential damage caused by drilling mud and cuttings discharges and are legislating accordingly. In addition to these legislative pressures, increasing demands are placed on fluids as the industry drills more extended reach, horizontal and high temperature/high pressure wells. These new challenges are in addition to existing ones - such as the need to control reactive shales, provide good fluid loss control and minimise formation damage - which remain critically important to the success of a well. Given these requirements asked of the fluid, many operators are convinced of the benefits of continuing to use oil based mud (OBM). Hence the industry, including companies such as BP, is committing considerable resources to developing ways of using OBM which comply with good environmental practices. These methods, such as cuttings cleaning and cuttings injection, are discussed by Minton, 1992 and Minton, Begby et. al., 1991. Another approach is to develop water based muds (WBM) which have little environmental impact but offer performance closer to OBM than existing WBM. The search for such fluids is being aggressively carried out by service companies and many operators. The final outcome of these studies is likely to be that a mix of options - water based muds, cuttings injection and cuttings cleaning - will be practicable and the final choice will be governed by a cost and risk analysis, local conditions and the preference of individual operators or their contractors. In any event, the use of cuttings cleaning or injection is unlikely to be practical for large hole sections in exploration and appraisal wells where a suitable annulus does not exist for injection and where the large volume of cuttings precludes the use of cleaning technology. In these situations the effective use of water based muds may be the best technical and economic solution. If water based muds are to be used successfully they must satisfy a number of criteria: From a technical standpoint: They must provide good shale inhibition. This is an essential requirement in many areas, including the Gulf of Mexico and much of the North Sea, Far East and CIS. If these muds are to be used in extended reach and horizontal wells they must be highly lubricating. P. 453^

Influence of Low Molecular Weight Polymers on the Rheology of Bentonite Suspensions

“…Low molecular weight synthetic ethylene-oxide based surfactants have been found to exhibit an inhibiting effect on the dispersion of shale cuttings [3] and [4]. The complex formulation of these suspensions have made it difficult to explain the influence of a particular component on their rheological behaviour.…”

Shale problems and water-based drilling fluid optimisation in the Hassi Messaoud Algerian oil field

“…In WBM, poly-(glycerols) and poly-(glycols) (abbreviated in the following as glycerols and glycols) have been widely applied in shaledrilling fluids (Chenevert, 1989;Bland, 1991;Bland et al, 1995;Downs et al, 1993;Cliffe et al, 1995;Reid et al, 1993;Twynam et al, 1994). They prevent cuttings from dispersing into the medium (Bailey et al, 1994).…”

“…They prevent cuttings from dispersing into the medium (Bailey et al, 1994). Therefore, they increase drilling rates (Reid et al, 1993;Cliffe et al, 1995).…”

“…-X-ray diffraction (XRD) analysis to determine qualitative mineral content, -Cation exchange capacity (CEC) and methylene blue test (MBT) to evaluate reactivity and shale factor of drilled cuttings. The MBT method was recommended by API 13I, Section 11 (2003), -A gravimetric swelling test (GST), used to measure water and ion motion during shale/mud interaction (Zhang et al, 2004), -Capillary suction time (CST) for determination of filtration properties and salt concentration optimisation (Wilcox et al, 1987), -Penetrometer to estimate the degree and the depth of softening (Reid et al, 1993) or "Bulk Hardness Test" designed to give an assessment of the hardness of shale following exposure to a test fluid (Patel et al, 2002), -Dielectric constant measurement (DCM) to quantify swelling clay content and determine specific area (Leug and Steig, 1992), -Triaxial test for pore pressure measurements, carried out in downhole simulation cell (DSC) for compressive stress/strain behaviour (Salisbury and Deem, 1990), -Oedometer test for pore pressure modification and chemical potential influence (Bol et al, 1992), -Slake durability test (SDT), a standard method originally used in geotechnical studies when measuring the weathering and stability of rock slope: ASTM D 4644-97 (ASTM, 2000), reapproved 1992 (Likos et al, 2004), -Jar slake testing, a qualitative method designed to evaluate shale relative durability in contact with a given fluid. Wood and Deo (1975), Lutton (1977) describe details of this method using six indices, -Differential strain curve analysis (DSCA) for in-situ measuring stress orientation and intensity (Fjaer, 1999), -Hot-rolling dispersion test (shale disintegration resistance or cuttings dispersion test), the most widely used technique in optimising drilling fluid.…”