Abstract

A high performance water based mud (HPWBM) system has been used successfully to address a combination of drilling challenges faced in the Middle East. Drilling problems encountered in the area typically include shale instability through pressure transmission effects, swelling clay-stone, bit balling, drill-string accretion, differential sticking over tight gas permeable sands and down-hole losses.

All these challenges can be very difficult to overcome with conventional water based mud (WBM) systems and can prove very expensive in terms of lost mud, lost down-hole tools, non performance rig time, side-tracks or ultimate failure to meet well or section objectives.

The HPWBM system was introduced to provide considerable improvement in WBM performance and also provide an environmentally benign alternative to oil based muds (OBM) while emulating OBM drilling performance attributes. Recent applications in the Middle East have proved that the HPWBM system can be applied as an alternative to OBM, successfully achieving the objectives of the sections while providing drilling performance comparative to OBM.

This paper discusses the technical features of the HPWBM system, gives an outline of previous applications and presents detailed case histories of the more diverse applications of the system and its components in wells in the Middle East, while comparing performance to offsets drilled with conventional WBM and OBM.

Introduction

As fields mature and the search for new oil and gas reserves continues, operators on the whole are increasingly moving towards drilling more challenging well profiles. Typical well profiles ever more frequently present challenges such as extremes of drilled depth, temperature, pressure, horizontal step out and extreme water depth to name but a few. In most cases, the common drilling problems found in less complex wells are usually exacerbated by increased complexity of well design.

Conventional WBM is often excluded from consideration in challenging wells due to the technical shortfalls associated with these systems. This tends to make OBM the system of choice due to the inherent technical benefits derived from running a continuous organic phase which alleviates many of these problems. However, where there are environmental drivers in place, operators often face a dilemma in balancing the performance requirements for the well with these environmental, economic and logistical drivers. In such circumstances a HPWBM can become an attractive alternative option.

In response to operator's requirements, the drilling fluids industry has placed great emphasis on the development of high performance water based fluids as performance driven alternatives to conventional WBM and as environmental and economically driven alternatives to OBM. This paper presents a unique high performance water based mud technology, discussing its technical features and its diverse application in the Middle East.

HPWBM Functionality

In the conceptional phase of the HPWBM, the drilling performance attributes of invert emulsion systems were examined, essentially identifying the technical features which make OBM the fluid of choice in most challenging wells. These were key areas in which conventional WBM's were generally considered inferior or deficient and were used as design criteria for the HPWBM with the aim of emulating the drilling performance of invert emulsion systems. The key attributes were identified as:

  1. shale stability through reduced or reversed pressure transmission effects,

  2. suppression of reactive swelling clays,

  3. improved cuttings encapsulation and solids removal efficiency,

  4. minimizing differential sticking tendencies,

  5. maximizing rate of penetration (ROP) and

  6. minimizing torque and drag.

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