Waterflooding is a recovery process that typically demands a high level of surveillance and remediation capability. This is because the geological complexity is often underestimated at the outset and the initial development concept is therefore rarely fully optimized. The well types and systems typically employed for deepwater developments often render this capability difficult to deliver. Furthermore, in order to ensure success, connectivity and sweep needs to be assured on the anticipated injector-producer well spacing. As developments move into deepwater, project economics place significant constraints on well numbers thereby developing tension between well numbers and connectivity.
This paper discusses the critical success factors for waterflood developments and discusses the means to ensure successful application of this recovery process in the deepwater setting.
The maturation of subsea well completions technology over the last four decades has enabled the development of fields in ever deeper and more hostile environments. This expansion has been facilitated by the maturity of conventional oil producing provinces and a buoyant market, which has driven operators to seek to develop reserves in marginal environments.
The technology development has driven exploration activity to ever more hostile environments - the average water depths for subsea installations have increased from an average of 410 ft in 1989 to over 1,180 ft in 1999. The trend continues, with some 55% of the subsea installations in 2005 beinginstalled in more than 1,500 ft of water.
The mushrooming of deepwater field developments has occurred despite the very significant development costs associated with such projects, presenting major economic hurdles. These challenges become even more significant when considering a waterflood development. It is important to recognise that the difficulties associated with waterflood are not only related to increases in cost. Historically it is fair to say that many waterfloods have produced water much earlier than originally anticipated. Surveillance, and subsequent flood optimisation, have therefore been seen as basic features of many waterfloods and these become much more difficult activities in subsea developments.
Surveillance requirements, however, represent just one of the significant issues to be managed for a subsea waterflood development. This paper addresses the relevant factors in some detail such that subsea waterflood developments can be approached in a rigorous and effective manner.
Channelised turbidite systems are very frequently encountered in deepwater environments. The development engineer working on maturation of such reservoirs faces a dilemma in that optimal recovery will be best served by a large number of wells but increasing the well stock is likely to compromise economics given the very significant well costs in such an environment. These pressures become even more crucial in waterfloods, given that injectors are also required. Given the pressures on well numbers, there is a premium on getting a large, but still effective, well spacing between injectors and producers.
