Exploration for Disorder
Authors: Morrison Graeme 
Published: April 2018

Two fundamental building blocks support the concept of exploration for disorder. The first building block is a sequential chain of petroleum system events resulting in a lognormal field size distribution. Output from the first building block becomes input to the second. The second building block is the intersection of multiple petroleum systems (prospects) in one exploration well or by multi-well exploration campaign. This second building block utilises the Central Limit Theorem whereby an aggregation of lognormal prospect distributions tends toward a normal field size distribution.

Exploration for disorder in practice is characterised by: Targeting multiple stacked reservoirs or multiple fluid phases in one exploration wellTargeting a field being the product of more than one sequence of petroleum system eventsBoth 1 and 2 above operating collaboratively.

The benefit of exploring for disorder is that the geological earth delivers, in the limit, a normal field size distribution and an exploration probability of success of 50% respectively supported by the Central Limit Theorem and Binomial Probability Theory. That is, the Central Limit Theorem dictates that the exploration probability of success cannot exceed 50%. These attributes contrast with exploration for ordered events which are allocated both a probability of success less than 50% and a lognormal field size distribution [according to Binomial Probability Theory]. Exploration in tune with the disordered geological earth delivers the highest probability of success.

Operating in parallel, gross rock volume (GRV) exists in a state of maximal entropy, hypothetically characterised by a normal distribution. Hypothetically, smaller GRV structures have a higher probability of being filled-to-spill resulting in a normal field size distribution for smaller fields. That is, smaller GRV structures require a lower volume of migratory hydrocarbons to fill-to-spill. Conversely, larger GRV structures may experience a wide range of fluid-fill variation thereby forming a lognormal field size distribution within the framework of a hypothetical, normal GRV distribution. This hypothesis was tested by Statistical Experiment.

Exploration for disorder is manifest in disruption to the monotonicity of creaming curves. It is expected that creaming curve disruption is caused by: An unplanned event (risk exposure): in a positive sense the geological probability of success (GPOS) and/or pre-drill GRV estimates fail to act as a proxy for field size and a larger-than-expected field is discovered; pre-drill field size estimates typically have a plus or minus one order of magnitude error bandDesign: the monotonically-diminishing lognormal field size creaming curve is disrupted by exploring for disorder; discovered field size jumps from a lognormal to a normal creaming curve.

A conventional lognormal field size creaming curve may encounter a "false summit" at the point where the discovery of small to medium field sizes coincides with: Low GPOS values (&lt;50%), and/orA field size sample-variance minimum.

The term "false summit" implies bypassed exploration potential. Exploration for disorder may then be utilised to fulfil exploration potential.