About Missed Pay

A definition of missed pay is “unrecognised or under-evaluated reservoir rocks that contain producible hydrocarbons”.

Missed Pay is a common, albeit not well documented, occurrence in exploration wells. It is rare for a hydrocarbon accumulation to be recognised as an oil or gas discovery by just one well. Statistics collected over a number of decades show that on average, up to four wells on a structure, not including appraisals, are required to find reserves greater than 100 MMBO. In many cases, the data or interpretation discrepancies in a well were too great to be unravelled and consequently, projects may have been prematurely abandoned, often for entirely non-technical reasons. There are some spectacular examples of the genre including North Field in Qatar, Elmworth in Canada, Cuisiana in Colombia and South Morecambe in the UK. MPX believes there are many remaining opportunities, currently classified as dry holes, which may actually be major hydrocarbon accumulations, merely requiring their recognition.

The Geologic Chance Factor (GCF) is defined as the chance of producing a significant flow of hydrocarbons from any reservoir or prospect. It is generally made up of three risk components: the trap definition and associated migration pathways; the source rock presence, quality and maturity; and the reservoir presence, thickness and quality. Historically, the UK Southern Gas Basin has a 20% success ratio, rising to 35% with 3D seismic, and the Central Graben has success ratios of 30%, rising to over 40% in the areas of mature source rocks.

The table below indicates how the recognition of missed or bypassed pay can dramatically change geological chance factors from the ‘normal’ exploration risk category to a different league of lower risk.

Type

Characteristics

Risk Factors

GCF

Missed pay

Hydrocarbons to surface.

How big?

What problem must be
solved to flow the well?

80-90%

Good indications of H/C’s or other anomalies.

How good are they?

What do the Logs/shows tell us?

Are there analogues?

40-80%

‘Normal Prospect’

Properly worked geological and geophysical data.

Good historical success in mature basin.

Trap?

Migration and source?

Reservoir presence and quality?

20-40%

Geologic Chance Factor (in Exploration)

Additionally, a significant number of anomalous wells tend to be older and may have been originally defined on 2D seismic, so are normally on larger structures than are currently being drilled. In this manner, the missed pay concept is capable not only of changing the prospect risk category but also rejuvenating the normal creaming curve for any particular play in any basin. The figure below shows the creaming curve for the Paleocene play in the Central North Sea. It can be seen that the discovery of the Nelson Field (originally drilled by Gulf in 1968 but actually discovered by Enterprise in 1986) creates a step change in the rate at which volumes are discovered. The resulting profile is similar to the one observed earlier in the life of the play.