Water-Based Drilling Fluid for HT/HP Applications

Abstract

The superior performance of invert emulsion fluids in challenging drilling operations such as HT/HP wells makes them the preferred fluid for such applications. However, there are instances such as drilling in environmentally sensitive areas, or where costs and logistics become prohibitive, where their use is undesirable. In such circumstances, a high-performance water-based drilling fluid is the only option available. A main challenge in developing a water-based fluid for such applications has been to maintain the stability of key fluid properties such as rheology and fluid loss at temperatures in excess of 130°C. Conventional additives, such as biopolymers or synthetic polymers, either become ineffective at such high temperatures or generate too high a rheology when used in quantities needed to curb fluid loss. This paper discusses a novel water-based drilling fluid system in which the synergy of the key fluid components produces a stable rheology and low fluid loss at temperatures approaching 200°C. Furthermore, by balancing the components of the novel system, fluid rheology can be controlled to meet the hydraulics and hole-cleaning demands of the drilling operation.1, 2 Introduction Today, an increasing number of drilling scenarios involve deeper and hotter reservoirs, complex well geometries and increasingly more stringent environmental requirements. These call for a new generation of high performance water-based drilling fluids, which can offer better drilling hydraulics (pressure losses and cuttings transport), high-temperature rheological stability, fluid loss control, shale stabilisation and lubrication. From a rheology point of view, the best fluid systems available to date are those that offer a high degree of shear-thinning to reduce friction losses and improve hole cleaning. These are based typically on biopolymers (e.g. xanthan and scleroglucan gum) or certain organic mixtures. While the most effective polymers for rheology control are those with high molecular weight (millions of Dalton), lower molecular weight polymers, frequently used for fluid loss control, can also have an effect on rheology. Thus, historically, control of rheology and fluid loss has required a fine balance between these two types of materials. At temperatures up to 130ºC biopolymers and organic mixtures are effective in controlling the rheology, but at higher temperatures stability problems set in and synthetic polymers must be used. Synthetic polymers, mainly polyelectrolytes, have good temperature stability but generate high plastic viscosities. This problem, which may be intensified by the high solids fraction of heavier drilling fluids, can lead to large pressure losses in narrower well sections. The conventional approach for generating and controlling drilling fluid rheology utilises various additives for the purpose of supporting and carrying the weight material and drill solids. To overcome the limits presented by such additives - biopolymers (temperature stability) and polyelectrolytes (poor shear-thinning and high plastic viscosity) - a different approach is needed. In the new approach described here, the polymers and the weight material are selected such that they both contribute to the generation and control of a highly shear-thinning, thermally stable rheology. Such improvement results from a synergistic interaction between the polymers and the weight material and requires polymers with: moderate molecular weight (to avoid excessive plastic viscosity), low charge density (charge on polymers increases backbone rigidity with impact on plastic viscosity; polyelectrolytes are more sensitive to salts, drilled solids and cement contamination) and stability at high temperatures (up to 180°C). Polymers that satisfy the above criteria produce relatively low viscosity if used on their own, which may not be adequate for suspending the weight material and for cuttings transport. However, when combined with a weight material with a specific surface charge, they produce highly shear-thinning aggregates with good suspending capacity. Figure 1 illustrates the conventional way of generating viscosity (1a) and the new approach (1b).

Formation Damage Caused by Improper Mn3O4-Based Filter-Cake-Cleanup Treatments

“…Mn 3 O 4 provides low rheological properties and equivalent antisag behaviour (Kleverlaan and Lawless 2004;Carbajal et al 2009). Tehrani et al (2007) noticed that Mn 3 O 4 -based drilling fluid might undergo a degree of flocculation and produce higher plastic viscosity values upon heat aging. To avoid agglomeration of Mn 3 O 4 particles at high temperatures, Mu et al (2006) suggested synthesizing Mn 3 O 4 particles using H 2 O 2 as an oxidant and starch as a capping agent.…”

“…They also compared formation damage by solids invasion in various drilling fluids, including Mn 3 O 4 -based fluids. However, it is reported that Mn 3 O 4 particles aggregate up to 20 lm in aqueous and oil-based fluids (Svendsen et al 1995;Tehrani et al 2007). Accumulation of these aggregates in the critical near-wellbore region is not desirable, and can result in stuck pipe during drilling operations.…”

Effect of Nanofluids of CuO and ZnO in Polyethylene Glycol and Polyvinylpyrrolidone on the Thermal, Electrical, and Filtration-Loss Properties of Water-Based Drilling Fluids

“…Thus, the prepared nanofluids added in drilling mud will yield benefits in stabilizing the viscosity and in cooling the drilling mud. It is worth noting that researchers at the National Energy Technology Laboratory are designing an environment-friendly nanofluid for oil and gas exploration and drilling that can withstand the high temperatures, as well as the highly-toxic, corrosive hydrogen sulfide gas that diffuses into drilling fluids in deep and horizontal wells during drilling operations (Tran and Lyons 2007). Their study indicated that there is a need for the development of novel nanofluids for drilling-fluid design to satisfy various operational requirements.…”

Innovative Chemistry for Drilling Fluid Additives

“…[2][3][4] There have been extensive researches reported by many institutions on the development of such high performance drilling fluids. 1,[5][6][7][8] Although we are conducting research and development on a range of novel drilling fluid additives for these demanding applications, a synthetic rheology modifier is the focus of this presentation.…”

“…[10][11] Polyelectrolyte-type rheology modifiers, however, can provide much better thermal stability, often possess poor shear-thinning properties and are sensitive to salt and drill solids with high plastic viscosities and shear degradation. 1 A desired rheology modifier for HTHP drilling should possess similar rheological properties to xanthan gum (e.g., high shear thinning) with enhanced salt tolerance and thermal stability. A high degree of shear-thinning and excellent suspension power of the weighting agents are key requirements in developing the new class of synthetic rheology modifier.…”