Mud Clean-Up in Horizontal Wells: A Major Joint Industry Study

Abstract

This paper describes a major joint industry study into the effectiveness of mud clean-up techniques for horizontal wells involving eight oil and service companies. Experimental work was carried out on a small scale laboratory clean-up rig to quantify mud damage and test breaker effectiveness. Large scale flow loop testing was used to evaluate overall clean-up techniques including displacement efficiency and damage to pre-packed screen completions. Tests on a wide variety of mud systems showed surprisingly little difference in the performance, from a formation damage perspective, on clean sandstone cores. Oil based muds were, however, found to produce less damage than water based muds. A range of breakers were tested with each mud system. There was a large variation in the results of breaker testing. with breakers, unexpectedly. sometimes causing an increase in the pressure required to break through mud filter cake and/or formation damage. Whole mud was found to cause significant damage to pre-packed screens; this damage was sometimes, though not always. removed during clean-up. Poorly centralised screens were found to result in large amounts of mud and debris on the low side of the hole. Introduction Horizontal wells are increasingly used in field developments to maximise well productivity, access reserves, or reduce water and gas coning by reducing drawdown. These benefits of horizontal wells can only be attained if all well sections are flowing without significant near wellbore damage. Most horizontal wells are completed open hole i.e. without a cemented and perforated liner. These open hole horizontal wells, which are typically completed with prepacked screens or slotted liners, differ from conventional cased and cemented liners in two important ways:–Oil or gas must be produced through mud filter cake and mud induced formation damage as perforations are not shot through the damaged layer.–Sand face completions such as pre-packed screens designed for sand control are themselves susceptible to damage from the mud system. A variety of specialised mud systems and clean-up techniques are used to try to minimise mud damage or remove it during well completion operations. The most common approach is to use a brine based mud system with an acid or water soluble weighting agent and then use acid breakers to dissolve filter cake solids and polymers. Brine is used to reduce mud solids loading and new systems are continuously being developed to extend this low-solids approach to higher mud weights; however, little work has been carried out to establish the need for, or the effectiveness of clean-up procedures. Radically different approaches to clean-up have been applied to the same mud system with apparent success. Also, wells in which little or no clean-up was attempted, have been completed with minimal damage. To address these issues an eight partner joint industry project was set-up to investigate mud clean-up in horizontal wells. A programme of experimental work has been conducted that studied the clean-up of a number of different mud systems, using both laboratory and large scale equipment. Additionally, large scale experiments were carried out to study the displacement process in horizontal wells. The objective of the project was to try to understand the parameters which control mud damage and its clean-up with breaker systems and thus allow a more systematic approach to fluids selection and the design of horizontal well completion operations. This paper describes the main findings of this joint industry project. Work Programme The work programme for the joint industry project consisted of seven test series. Each of the first six test series investigated the damage and clean-up behaviour of a specific mud system with a number of breaker systems. Both small scale laboratory tests and large scale flow loop tests were used. The final test series was a displacement study. P. 801

An Investigation of Formation Damage Characteristics of Xanthan Gum Solutions Used for Drilling, Drill-In, Spacer Fluids, and Coiled Tubing Applications

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Despite all the efforts, questions still remain regarding the formulation of optimum fluid composition to minimize productivity impairment due to formation damage.…”

“…Fluid loss control in solids-free brines is generally achieved by; increasing the viscosity of the fluid [5][6][7][8][9][10][11][12][13][14][15][16] and developing internal/external filter cake using lost control additives 17 . In a recent study, Svendsen et al 18 has shown that extensional viscosity can be successfully used to establish an internal filter cake in association with a coiled tubing drilling fluid application.…”

Design Methodology for Selection of Horizontal Open-Hole Sand Control Completions Supported by Field Case Histories

“…The generally poor level of clean-up led to serious plugging problems in many wells. [11][12][13][14] Although there were variations between operators, failure rates of 50% and higher occurred in a number of early projects using standalone screens for sand control in horizontal wells. 1 As better drill-in fluids were developed and better clean-up techniques implemented, horizontal well failure rates declined to an industry average of around 15 to 20%.…”

Hybrid Washer Fluid for Primary Cementing

“…The issue of washing the annular space covers many scientific aspects. These are the rheology of drilling fluids, fluid mechanics, the action of chemicals (surfactants), and the action of chemical additives during cement slurry hydration [3][4][5][6][7]. The development of techniques and technology has not yet made significant progress in improving well bonding.…”

“…In addition, the issue that affects the quality of sealing the annular space is the adhesion of the hardened cement slurry to the rock through the remains of the remaining mud cake. The bonding of the joint between the rock and hardened cement slurry is affected by the thickness and consistency of the mud cake [2,4,[7][8][9]14,15,31]. The thickness of the mud cake depends on the degree of washing, as well as the time and intensity of washing.…”