Ocean Floor Wellhead Arrangement for Hydraulic Oilwell Pumping
Authors: Coberly C.J. , Ralph R.G. , Nelson C.C. 
Published: December 2007

Hydraulic pumping offers a solution to the problem of producing ocean floor-completed wells. Present hydraulic pumping equipment and field experience are applicable to producing undersea wells. This article presents four possible designs of wellhead equipment for undersea operation.

Introduction

In the evolution of ocean floor well completions, great amounts of ingenuity, technical effort and money have been expended to provide definite answers to current operating problems and to explore a wide range of anticipated problems. Naturally, any operator of deep water production will defer as long as possible the use of any type of artificial lift. The obvious difficulty of locating and supporting the pumping equipment and the problem of pulling subsurface equipment for maintenance may seem insurmountable. This article shows that ocean floor wells can be produced at any water depth by the application of hydraulic pumping with practical, available equipment that has been tested and proved. To orient this discussion, background information on hydraulic pumping and its application to the conditions relating to ocean floor completions are given.

Hydraulic Pumping System

A hydraulic pumping system consists of four basic units: power fluid pump, pump control station, wellhead station and bottom-hole pump. The power fluid pump provides high-pressure fluid for operating the bottom-hole pump. The fluid may be produced oil or-by a recent development-fresh, produced water or sea water. The second basic unit is the pump control station consisting of a header manifold with a pressure controller and power fluid control valves; the latter regulate the speed of the pump in each well. The station provides a means of metering the power fluid delivered to the wells and a means for directing the power fluid to the wellheads. It may also provide valving means for circulating the pump in and out of the well. The station may be located at any point between the power fluid pump and the wellhead?The third unit is the wellhead which provides a means of inserting and removing the bottom-hole pump from the well tubing. A pump catcher is incorporated in the wellhead cap to secure the pump once it has been circulated up to the wellhead. The wellhead also provides a means of connecting the surface lines from the pump control station to the corresponding well tubing lines.

The fourth and last unit is the bottom-hole pump consisting of a reciprocating-type fluid engine connected directly to a fluid pump. The outside diameter of the unit is such that it can be inserted into and operated within the well tubing, the pump being located approximately at formation depth when in operation. The pump may be circulated in and out of the well tubing hydraulically as a Free Pump,* thus eliminating the need of a pulling unit. The four basic units are interconnected by means of tubing to complete the hydraulic pumping circuit.

Applicable Field Experience

For many years the hydraulic pumping system has been used in multiple-well operations with as many as 80 wells being operated from a central power plant. The controls for each well are located at the central power plant, at satellite control stations or at the wellhead, according to the individual requirements of the installation. Well spacing has been up to 160 acres and surface line lengths as long as 3 miles. Lake, reservoir, marine and river installations are using conventional hydraulic pumping equipment. In some installations, the wellhead is submerged during periods of high water, however, the usual practice is to extend the wellhead above the high-water level so that it is accessible at all times.

Central power plants for these installations are located on shore, on offshore islands or on platforms. The maximum offshore distance of platform or island installations has been 20 miles, with service provided by either boat or helicopter. Power fluid and production lines from the platform servicing these wells are submerged and, in most cases, are run on the bottom.

JPT

P. 983ˆ