Early Production Systems

Abstract

Summary This paper presents alternative systems for developing production from offshore tracts, where it may be production from offshore tracts, where it may be desirable to depart from so-called conventional platforms. These unconventional systems may be considered platforms. These unconventional systems may be considered for reasons of water depth, economics, limited reserves, drilling and development problems, and/or platform construction considerations. The objective is to increase production during the early life of the project to accelerate production during the early life of the project to accelerate payout. The alternative systems discussed here include payout. The alternative systems discussed here include (1) predrilling through templates while a fixed platform or tension leg platform (TLP) is being constructed, (2) drilling subsea wells for connection to a semisubmersible drilling vessel converted to production service, and (3) subsea wells connected by a monobuoy system to production facilities placed on a captive tanker with either production facilities placed on a captive tanker with either pipeline or shuttle-tanker offtake capability. pipeline or shuttle-tanker offtake capability.In any of these systems the practical aspects of the operation must be emphasized. The more complex the system becomes, the greater the opportunity for malfunction and associated production downtime and loss. Introduction Before 1973, when world supplies of crude oil were readily available, the need for early production systems was less prevalent. Although there was an excess crude supply during 1981, a high-demand, short-supply situation may develop in several years. This, coupled with ever-increasing costs in all parts of the world, makes it necessary to consider all alternatives for exploiting crude reserves, especially those for which economics may be marginal. The total world oil and gas reserves will be increased by applying these techniques to develop otherwise uneconomical tracts, particularly in deep waters. During the past 10 years, more than 12 various platform systems have been installed to provide early platform systems have been installed to provide early production and hence early revenue. All types of systems production and hence early revenue. All types of systems we discuss here can be considered operational and not experimental. Among these are two Conoco operations in the North Sea: the Murchison platform, now on production with two subsea well producers, and the Hutton production with two subsea well producers, and the Hutton project, which includes predrilling through a template project, which includes predrilling through a template located on the seabed. Existing Systems At Murchison, several exploratory delineation wells were drilled, two were completed as subsea producing wells and one as a water-injection well. These wells were completed subsea, with the flowlines connected to the fixed platform immediately after installation (Fig. 1). This provided the platform with two wells, capable of producing more than 10,000 B/D (1590 m3/d) each, producing more than 10,000 B/D (1590 m3/d) each, which became the early producers for the complex. This installation proved the viability of new pipeline and wellhead connection techniques that will prove applicable in most new installations at nearly any water depth. During the first 6 months of production, these two wells contributed 2.1 million bbl (0.33 × 106 m3) or 29 % of the 71 million bbl (1.14 × 106 m3) produced by the platform. The Hutton field in the North Sea will feature the first TLP installed for oil drilling and production. The TLP will consist of a semisubmersible vessel moored to the ocean floor with steel tethers. Drilling will be through a template on the ocean floor by predrilling several wells with a standard semisubmersible drilling fig and by drilling remaining wells with a rig mounted on the TLP vessel. The configurations will be similar to those shown in Figs. 2 and 3. The subsea template, built to accommodate 32 wells, was installed in May 1981. JPT P. 2523