Wellhead Location Technique
Authors: Moody Cecil Douglas 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the SPE-European Spring Meeting 1976 of the Society of Petroleum Engineers of AIME, held in Amsterdam, The Netherlands, April 8–9, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal, provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

The paper discusses the technique of using Side Scan Sonar for Wellhead relocation enabling a rig to be put in position quickly saving rig and divers time. put in position quickly saving rig and divers time

Introduction

Since the late 1960's, side scanning sonar has become a widely used, often indispensable tool for sea floor engineering and survey activities.

This sophisticated acoustic technique has the unique ability to create accurate, continuous, wide-area "pictures" of 3-dimensional sea floor features and contours. As a result it permits quick and economical acquisition of information not readily available through any other type of acoustic instrumentation.

As with most other under-water sonar devices, Side Scan Sonar derives its information from reflected acoustic energy. In operation, however, it bears a marked similarity to radar, in that it produces a continuous, coherent plan view of a relatively broad scanned area. A set of transducers mounted in a compact tow fish generate the high-power, short-duration acoustic pulses required for the extremely high resolution of the system. The pulses are emitted in a thin, fan-shaped pattern that spreads downward to either side of the fish in a plane perpendicular to its path. As the fish follows the tow vessel's track, this beam scans a bottom segment ranging from the point directly beneath the fish outward as far as 500 point directly beneath the fish outward as far as 500 metres to each side.

Acoustic energy reflected from bottom (and waterborne) discontinuities is received by a set of transducers, amplified and transmitted as electrical energy to the towing vessel. There it is amplified, processed and converted to hard copy by the Side processed and converted to hard copy by the Side Scan Recorder.

The resulting output is essentially a topographic mop providing a detailed representation of ocean floor providing a detailed representation of ocean floor features and characteristics. Good acoustic reflectors rocks. ledges, metal objects and sand ripples - are represented by darkened areas on the record. Depressions and other features scanned from the acoustic beam are indicated by light areas. An experienced observer can interpret most records at a glance, recognising not only significant features and objects, but often more subtle data such as the composition and relative hardness of the bottom and the shape and condition of submerged objects such as wellheads.