A Combined Deterministic‐probabilistic Method of Estimating Undiscovered Hydrocarbon Resources

Abstract

Play analysis is used to delineate areas containing geologically similar discoveries and prospects. The yet‐to‐find (YTF) recoverable resource for a conventional play can be predicted using deterministic scenarios utilizing the fact that discoveries within a part play (or common risk segment) can be fitted to a lognormal distribution. Assuming the part play works, a YTF scenario can be made with estimates of (i) the number of drillable prospects, (ii) the average prospect risk, (iii) the resource size of an upside discovery (based on the evaluation of a favoured prospect), and (iv) a downside resource from an implied P99 volume (based on historical data or calculation). A range of YTF is then developed using low, median and high case scenarios. The value of the different scenarios can be estimated provided a minimum economic field size for a generic prospect is available plus a pre‐drill net present value for an average economic discovery. Useful reality checks of YTF estimations include the historical discovery rate, the areal density of traps in analogue settings, the historical average discovery size and the total estimated recoverable resource per unit area. YTF from prospect inventories using Monte Carlo simulations tend to focus on mature areas and are biased to outcomes where all pre‐drill models are correct, unless the prospect sizes are adjusted to account for discoveries which are smaller than predicted by seismic interpretation. YTF estimates will change as information about the play evolves, meaning that it is important that the calculations are kept relatively simple and easy to adjust as new well and seismic data becomes available.

The Prospect Area Yield (Pay) Method: A Remedy for Over‐optimistic Volumetric Estimations in Conventional Petroleum Exploration

“…One important control is to check whether the outputs are consistent with historical data for analogous discoveries (Sluijk and Parker, 1986;Ofstad et al, 2000b and references therein;Milkov, 2017). For example, P99, P1 and mean resource volumes for the prospect are often compared to statistical data for discoveries in the play or in a relevant analogue play (Rose, 1998;Quirk et al, 2017). Where there is a mismatch, the probabilistic inputs are often adjusted in a trial and error process so that the outputs fall within a range which the evaluation team feel better represents near-minimum and near-maximum values for the prospect.…”

“…A useful property of plays is that both the recoverable resource and the footprint area of the smallest discoveries tend to remain relatively constant over time, at least in terms of the statistics for "near minimum" sizes, i.e. those belonging to the P99-P90 probability range (Rose, 1998;Quirk et al, 2017;Quirk and Archer, in press). The sizes of discoveries in this range vary significantly across different plays, a function of the quality of seismic imaging, economic filters and reservoir properties (Drew et al, 1988) and they provide useful indicators as to how small a prospect may be in a downside case.…”

“…The most useful play statistics relate to the size of discoveries -both the recoverable resource and the footprint area -as well as to derivatives such as area yield (Quirk et al, 2017). Amongst these data, small, sub-commercial discoveries are common.…”

“…In plays with robust direct hydrocarbon indicators (DHIs), the inferred P99 may be larger than usual because geophysical anomalies associated with small closures tend to be screened out rather than drilled (Quirk and Ruthrauff, 2006), meaning there is often a difference in the inferred P99 area of a non-DHI play (typically <2 km 2 ) compared to that of a DHI play (often >2 km 2 ). Another source of information on the size of discoveries, the footprint area, is a relatively underutilized statistic but it too can provide an invaluable guide to the downside within the same or similar plays (Quirk et al, 2017).…”

Play-Based Hydrocarbon Exploration Under Spatial Uncertainty Using Evidential Theory

“…Recently more researches were undetakened such as (Zhongzhen et al ,2017) which based on hydrocarbon accumulation factors analysis, including source rock, reservoir, trap, migration, seal and preservation have evaluated and ranked plays by using double factors method of resources-geological risks. (Quirk et al ,2017) investigated a combined deterministic probabilistic method of estimating undiscovered hydrocarbon resources or YTF 1 for a conventional play. This research proposes a GIS-based framework using Dempster-Shafer theory (Shafer, 1976) to manage spatial uncertainties in the hydrocarbon exploration play CCRS map.…”