Abstract

During a typical drilling process, many different types of drilling mud and associated drilling mud additives are used to control a variety of downhole problems. Drilling mud can include hydrocarbon-based fluids or waterbased fluids with components ranging from flocculants and shale control additives to walnut shells and straw for lost circulation. As newly drilled wells frequently require stimulation, it is imperative that compatibility of stimulation fluids with the drilling fluids and associated additives be demonstrated. There are a variety of reactions that can occur between both the drilling fluid and additive components and the stimulation fluid considered for use. This paper presents a systematic bench test process for evaluation and selection of proper stimulation fluids for use in removal of drilling damage. As well, illustrations of the potential adverse reactions that can occur between certain types of drilling fluids will be demonstrated.

Prior to the stimulation treatment, the Service Company should perform a suite of fluid compatibility analysis using a test method approved by the operating company. The operating company should create a ridged set of practical test procedures that apply to the formations the operating company works in. Not only does the quality of the stimulation fluid on location need to be ensured, but also it's compatibility with the formation rock, formation fluids, drilling mud and even a combination of all these items. These relatively simple bench tests can illustrate how the fluids will interact. If increases in viscosity, precipitates, sludge or emulsifying tendencies occur between the fluids at surface conditions, there is an opportunity that similar reactions may occur at bottom hole conditions.

By anticipating the possible side reactions that may occur prior to the treatment and simulating these reactions in the laboratory, potential down-hole problems can be avoided and the treatment can be given the opportunity to be an economic success.

Introduction

The drilling department's main goal is to make hole as quickly and as cheaply as possible. Typically, the mud program is in place prior to drilling, but multitudes of additives are available to solve unexpected problems that occur while drilling. After the well has hit total depth, there is often the necessity to stimulate the zone of interest. The first step is often to choose a low cost matrix acid treatment.

The interactions that can occur between the stimulation fluid, residual drilling fluid and filter cake take on a greater significance during a matrix acid stimulation due to the low injection rates and high degree of intermingling of fluids. The goal of all matrix acid treatments should be to ensure that the damage is bypassed or removed and conductive channels are created that allow formation fluid inflow. If the wrong treatment is initiated or the blend is not optimized, the damage created by the treatment could turn the work over into a technical and economic failure.

Service company's test procedures can vary considerably and can result in a vastly different stimulation fluid.

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