A significant part of any field development planning exercise resides in adequately quantifying reservoir uncertainty, particularly when information availability is limited. For marginal fields, accurate appraisal of the downside of a project becomes even more crucial, as different development options carry a significant probability of negative net-present-value and project economic viability relies on reservoir risk minimization.
It is then imperative to undertake a complete and detailed risk analysis, in order to identify key contributors to reservoir uncertainty, their combined effect and their impact on the final economic outcome. A thorough understanding of the risk setting can lead to resources being better focused, data acquired and creative solutions found, thereby mitigating the uncertainty and shifting the Gaussian distribution of recovery and net-present-value to the right. The evaluation and quantification of the impact of key uncertainty factors is exacerbated by the multiplicity of combinations in development options and can only be represented by a very high number of simulations. It is only with today's computing power and recent software developments, in stochastic data analysis and statistical optimization, that it is possible to quickly and exhaustively encompass all relevant uncertainty parameters.
The following case of a marginal offshore field in Angola illustrates the successful application of a stochastic planning approach in defining the optimum field development strategy. A novel workflow in stochastic analysis was applied allowing proper identification and mitigation of all relevant risk factors. This resulted in the determination of optimum surface facilities dimensions, well locations, drilling plans, wellhead structure locations, coring programs and logging suites. This methodology was key in establishing an economically viable option in this high cost, high-risk area.
The Morsa-West field was discovered in the early 80's, offshore Angola, and delineated four separate hydrocarbon-bearing accumulations with a total of eight exploratory and appraisal wells. The formation types vary from sand (S) to sandy dolomite (SD) to predominantly dolomite (D) with productivities ranging from fair to good depending on the different geological environment and the presence of tectonically created fractures.
The original operator attempted to put forward a viable development plan but had to relinquish operatorship as no economic solution was reached. Sonangol P&P, the operating arm of Sonangol, took it upon itself to investigate the development of this potential and completed a subsurface evaluation of the area. This evaluation concluded that five of the eight wells drilled encountered oil and the four confirmed accumulations could potentially be developed economically. Simultaneously, oil-bearing exploratory prospects were identified in the area providing further need for project implementation. Following this work, Sonangol P&P approached the Concessionaire and was granted the right to review the information and propose a field development plan for the Morsa-West area.
The following work is a culmination of the efforts, put forward by the Sonangol sub-surface Team, to develop what was previously labelled as a marginally economic field into a profitable venture for Sonangol P&P.
Definition of Risk Two types of risk exist at the Field Development level, Market Risk and Project Risk.
