Abstract

Major advancements have been made in the past decades to determine the effects from particle additions to drilling fluids. These additions affect wellbore stability, hole cleaning, sag stability, formation damage and back-production capabilities. Furthermore, optimum drilling fluid performance is strongly dependent on knowing the properties of the formation such that correct selections of drilling fluid additives can be made. Likewise, it is important to know if produced solids are drilled cuttings or cavings originating from unstable holes.

In field applications, there has been reluctance towards trusting solids control equipment as the only method for controlling the particle size distribution (PSD) and particle content of the drilling fluid system, since no real-time monitoring equipment has been available to produce the necessary measurements. The present paper describes a technique based on image analysis, which makes it possible to obtain such information in real-time. The method also provides valuable information for characterizing drilled cuttings, creating the basis for caving logs. A method for obtaining mineralogical data from the formation by analyzing the drilled cuttings by using Raman spectroscopy is also described. Field tests and laboratory studies demonstrate the potential of the techniques for improved drilling process control by continuously monitoring the particles in the system while drilling. Some of the elements in a drilling fluid process which are affected by the presence of particles are also described.

Introduction

Controlling drilling fluid parameters is important to obtain proper drilling performance. In order to achieve this, the fluid properties also need to be measured sufficiently accurately. Therefore, the industry has implemented a set of standards 1 describing which parameters to be measured and the methods of measurement. Optimum drilling fluid performance is strongly dependent on knowing the formation properties so that correct selections of drilling fluid additives can be made. Likewise, it is important to know if produced solids are drilled cuttings or cavings originating from unstable holes.

In field applications one has been forced to use the anticipated performance of solids control equipment as the only method for, at least to some extent, controlling the quantity and size distribution (PSD) of the particles in the system, since no laboratory or field instrument has been available to produce the necessary measurements. However, other techniques can be applied to continuously monitor the particles in the drilling fluid and the drilled cuttings. Techniques exist for describing the mineralogy of the cuttings, assisting a fast update on formation description. Furthermore, it is possible automatically to detect if there is potential for hole stability problems. The combination of these techniques provides a significant potential to increase the knowledge of how the drilling and production performance is affected by the solid addition to the drilling fluids.

This paper describes results from a field test were all the parameters above have been measured. Currently, most of the measurements on drilling fluid properties and cuttings properties are done manually. Most of these measurements can be automated by selecting suitable techniques. Such techniques have been evaluated in the present field trial. However, since this has been a test of laboratory prototypes, manual collection of samples have been made in order to evaluate the techniques with no focus on automatization of the sampling system at this stage. However, the sampling can be automated for all the tests conducted here. Finally, some of the elements in a drilling process which are affected by the particles in the fluid system is described with emphasis on wellbore stability, sag stability, formation damage and drilling fluid viscosity.

Solids control and particle size

Proper running of the solids control equipment and fully controlling the PSD and particle content of the drilling fluid is of the greatest importance to obtain the desired effects of the particle additions. Despite the importance of this aspect, little attention has been paid to ensure that the shaker screens have actual correctly set Cutt-point throughout the drilling process.

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