Drilling of multiple wells from offshore platforms has increased the accuracy requirements for directional surveying. To meet this need a 3-dimensional method of surveying wells to within one foot to 13 3/8 in. casing shoe has been developed. The basis of the equipment is an inertial system which consists of a gyro stabilized instrument cluster with three accelerometers measuring the displacements. The advent of inertial techniques has provided a means to complement monitor and improve provided a means to complement monitor and improve conventional survey techniques.

Introduction

The increased density of wells being drilled from offshore platforms, particularly in the North Sea has emphasized a need for more accurate directional survey techniques. Safe practice necessitates an increasing loss of production during concurrent drilling and production operations due to the uncertainty of hole position. The need to define bottom hole position is essential to avoid loss of well control. There has existed a source of concern arising from doubts about the accuracy of conventional surveys and the doubt that the position of a deep well could be defined with a horning device.

TECHNOLOGY

Given a doubt about the accuracy of conventional surveys there has been a need to define alternate systems. Inertial navigation systems have been developed for application in all weather combat aircraft and missiles. More recently they have been applied as survey equipment in artillery and topographical surveys. The navigation performance for aircraft is typically one nautical mile per hour - accuracy sufficient to assist transatlantic crossing - the system is, however capable of increased accuracy under different operating conditions.

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