Design and Synthesis of Shale Stabilizing Polymers for Water-Based Drilling Fluids

Abstract

Abstract Troublesome shales can cause costly downtime due to stuck pipe, hole-fill and even hole abandonment. Much research effort has been expended in an attempt to better understand shales and their interaction with drilling fluids. A combination of cations with water soluble polymers are known to effectively polymers are known to effectively stabilize many shale formations including combinations of potassium chloride with partially hydrolyzed polyacrylamide (PHPA). partially hydrolyzed polyacrylamide (PHPA). This paper will focus on general aspects of how PHPA and other polymers stabilize shales. In the stabilization of shales by various chemical agents, the specific mechanism by which polymers stabilize shales has not been studied in detail. A shale stabilizing mechanism based on polymer adsorption onto clay surfaces and polymer adsorption onto clay surfaces and how solution properties of polymers affect this mechanism, will be proposed. Several simple approaches to the design and the synthesis of improved shale stabilizing polymers for water based drilling fluids polymers for water based drilling fluids will be discussed. A commonly used shale disintegration test has been modified for use in screening many shale stabilizers. This test method is capable of generating statistically reproducible results and has provided some mechanistic information on shale stabilizers. Such information is valuable and has led to the design and the synthesis of a new improved polymer useful for shale stabilization in water-based drilling fluid systems. Introduction The clay containing shales which are common to oil exploration activities hydrate, swell, disperse and/or slough into the wellbore during drilling. Reasons for shale instability are chemical, mechanical and physical. Chemically, shale hydration, swelling and dispersion are examples of critical shale reactions. These reactions are aggravated mechanically and physically by the stresses of overburden pressure, geopressured shales, pipe rotation, and erosion due to mud circulation. These problems lead to hole enlargement, stuck pipe and balled collars and bits among other things; thus they have a major influence on the overall drilling efficiency and subsequent drilling costs. Among the various mud systems for dealing with troublesome shales is the potassium chloride/partially hydrolyzed polyacrylamide (PHPA) mud. Oil polyacrylamide (PHPA) mud. Oil based fluids, although very effective, are generally expensive and present environmental problems. Guidelines for choosing muds for drilling various types of shales have been suggested. It is the intent of this paper to explore why certain water soluble polymers stabilize shale formations and to discuss design considerations and synthesis of new improved polymers as potential shale stabilizers for water based drilling fluids. Reference will be made to some available commercial products that have been and are being used in the field for such purpose. P. 163