The development process of new technologies in drilling fluids has established that the fluid should have viscosity control and clays inhibition.Some other aspects as fluid loss control and grout thickness had become almost that decurrent of the action of the main products.The search of a highly inhibitive water-based drilling fluid (WBDF) system has been a continuous purpose in the drilling fluid industry.
We have designed and developed new materials that will improve the inhibition capacity of water-based fluid, besides favoring a complete rheology and fluid loss control of the system.Parameter viscosity reached great evolution in the last decades with the implantation of high performance polymer, capable of substituting the bentonite.Through this, the fluid with low solid became the key of the success in perforation fluids.
The developed system consists of an environment-friendly cationic polymer as shale inhibitor, a fluid-loss control, and a polymer that provides viscosity and gel structure.Components were designed for high performance water-based drilling fluids, and present the versatility to be used as much with industrial water, as seawater or saltwater, maintaining the fluid performance. This work will discuss some properties of this system, comparing with the traditional system used by Petrobras - Brazil.
The Drilling fluids play several functions in drilling well.If the mud properties are incorrect, safety and economics may be severely compromised.To each drilling fluid, its behaviors are major guarantee of drilling operation success[1–2].In selecting the most suitable type of drilling fluid, many different factors must be considered.What is required is a mud system that provides lowest overall cost of drilling each hole section.When drilling through the reservoir, the main purpose to minimize damaging reactions between the mud and reservoir.
Many problems are caused by incompatibility between water and shales.This may be solved by using oil/water emulsion mud or 100% oil mud.This isolates water from shales and prevents hydration[1,3].However, oil muds are becoming increasingly difficult to use in some areas due to environmental concerns and government regulations changes.Water-based drilling fluids (WBDF) may use various chemical inhibitors to control reactive shales.These special drilling fluids are formulated to provide lubricity, inhibition, solids suspension and borehole stability.They also have to protect pay zones by forming an effective filter cake to control fluid loss, stay intact during completion operations and clean up easily[4–5].
Several researches have been developed to minimize the shale hydration by WBDF.The KCl addition on these kinds of fluids works by changing places with sodium atoms in the clay structure and, as potassium ion is smaller than sodium ion, this causes the clay structure to shrink rather than expand1.A recent development is the use of soluble silicates in clay stabilization.These are soluble at high pH, but precipitate out of solution if the pH drops. Tiny amounts enter the pore space between crystals, the pH drops, silicate precipitates and form a barrier to further water penetration.Use of silicates seems to cause the clay to harden over time1.Systems using a blend between KCl and glycols as inhibitors in WBDF have been Applied7–8.In these systems, xanthan gum and dextrin were used as viscosifying and loss filtrate control respectively.Other useful chemicals include polymers.Clay crystals have electrostatic charges on their faces and edges.If a polymer molecule also has opposing charges along its length, polymer sticks to the clay crystal and prevent water from reaching it.This is the principle of water-based cationic drilling fluids.
The development of a WBDF, which could exhibit similar drilling characteristic to an invert emulsion drilling fluid, has been an ongoing endeavor of the drilling fluid industry[9–10].Different WBDF systems have been developed over the past ten years aiming to approach the drilling performance of an oil based mud.However, the developed fluids have not been completely successful in inhibiting the hydration of highly water sensitive clays.The cationic polymer systems used actually give a more oil based fluid-like inhibition.But, the cationic polymer toxicity (generally an organ chloride material) and their incompatibility with other anionic additives for water drilling fluids, have limited the system success.