Data Acquisition During Field Development: Proposal for a Niger Delta Field
Authors: John Udeme , Ogunjobi Abiodun , Lawoyin-Olajide Nike 
Published: July 2016

Data gaps identified during feasibility studies for oil and gas projects present a major source of uncertainty in the evaluation of oil and gas reserves. It could range from subsurface data such as velocity seismic profile (VSP), - petrophysical parameters, PVT properties to surface data such as appropriate cost database.

Subsurface data, especially for oil and gas asset development when compared to surface, appears to contribute the most uncertainty and is likely to impact on the business decision the most. To appreciate these uncertainties, low, best and high estimates were made during reserves calculation. In this work, high estimate was observed to be thrice as high as the low estimate number for both oil and gas recoverable numbers.

The impact of high uncertainty level in reserves estimate on business decision making, both for equity owners and potential investors can be quite huge and can be the difference between a Final Investment Decision and project execution for external funding. The gap is widened by lack of funding appetite arising majorly from both subsurface uncertainties and market uncertainties. In order to improve the value of the decision making process, these data gaps need to be closed or minimized. Closing these gaps to a large extent depend on the value to be derived from additional data to be acquired. A demonstration of this value is rarely undertaken by the engineers or Geoscientists, decision making to acquire more data is very difficult for business owners and quite often not approved due to cost implication despite the inherent rewards.

This paper demonstrates the process of understanding and identifying the subsurface data gap, quantifying the range of uncertainty resulting from these data gaps and their impact on resources estimation for a Niger Delta field development project. It is expected that the recommendations from this study will form part of an integrated approach to data acquisition during the early phase of the development of a field. In addition, the economic benefit of closing the uncertainty gap for the studied field is also demonstrated in this work using decision tree analysis.

Following a systematic approach, it was observed that for this field, uncertainty in Gross Rock volume estimation, principally due to lack of velocity data contributed to 34% of the large variance observed in the oil reserves probability distribution and 18.5% for variance observed in the gas reserves distribution. A major contribution to the variance came from porosity and water saturation. This is due to inability to acquire the neutron-density logs in two out of three wells drilled across the field as a result of hole instability and other technical challenges. It was recommended that two development wells (Shallow and deeper targets) could be used to acquire velocity/core data and full suite of wireline logs in the field. This is expected to reduce the uncertainty gap by about 75%. The additional cost of data acquisition for the purpose of further field appraisal was justified by demonstrating that the additional data proposed will improve the value of the asset.