WHAT IS THE PETROLEUM PLAY
In hydrocarbon exploration, favorable geological conditions are sought with a reasonable chance that a well drilled in the location will encounter a significant volume of hydrocarbons. The method by which Explorationists (the collective noun for Geologists, Geophysicists and Geochemists) evaluate the geological conditions is through a concept of the petroleum play. The petroleum play is a perception (or model) of how a specific region of the Earth's subsurface may be an appropriate target for exploration drilling. More specifically, how a:
•producible reservoir (the rock with its connected pore or fracture system),
•petroleum charge system (the source rock for the hydrocarbons and its migrationpath to the subject reservoir),
•regional topseal (the capping rock preventing migration out of the reservoir), and
•trap (the geological features defining the physical limits to the reservoir rock in thesubsurface)
may combine to produce significant petroleum accumulations at a specific stratigraphic level. The US Geological Survey defines a play as a set of known or postulated oil and (or) gas accumulations showing similar geological, geographical and temporal properties such as source rock, migration pathway, timing, trapping mechanism and hydrocarbon type. This essentially refers to already discovered fields rather that the conditions favorable for their discovery. In both definitions, the necessary attributes for a successful petroleum play are the same and are of fundamental importance to explorationists.
Explorationists within the operator (the oil or gas company that holds a license to explore on the behalf of a consortium of companies) are charged with identifying the 3-D distribution of the various elements listed above (this is termed play mapping). The basic data that are used for this purpose include:
•Outcrops where the rocks of interest come to the surface,
•Well data, where borehole measurements and samples of the rocks of interest areavailable,
•Seismic data (providing sub-surface imaging of the rock structure),
•Geological studies by government geological surveys or industry contractors,
•Information from discussions with professionals in other companies (scout data).
These data have to be synthesized and integrated into a series of play maps to show the general areas of interest for further consideration by operator management and consortium partners. Within these areas (usually large, from 10's to 100's or even 1000's of sq.km) the explorationists will also define specific leads (usually less than 10 sq.km) which can be identified and worked into prospects after further data collection or analysis. The operator may wish to drill prospects if a sufficient chance of success can be demonstrated. A lead is unlikely to be drilled without further work.
A prospect is an identified trap (structural or stratigraphic) which:
- has a reasonable chance of containing rock that has holes (i.e., is porous) which areconnected and can conduct fluid (i.e., is permeable),
- is older than the time which oil/gas was available (oil and/or gas migrates from asource rock on reaching thermal maturity),
- is in a location to which oil/gas could move (migrate)
- •is of sufficient potential size with enough confidence that oil will be found towarrant
- • drilling an exploration well.
These data have to be synthesized and integrated into a series of play maps.Within these areas (usually large, from 10's to 100's or even 1000's of sq.km) the explorationists will also define specific leads (usually less than 10 sq.km) which can be identified and worked into prospects after further data collection or analysis.
The decision to carry out any exploration work will depend on various factors at each stage. A play has to be identified before any exploration drilling starts. Initial surveying will depend on the potential of the play. Detailed surveying will depend on the size and number of leads identified. At any stage, the licenseposition with the licensing authority (usually government) has to be agreed. Licensing rounds are usually offers for competitive bidding from consortia.
The size of a lead or prospect and the likelihood of success are often linked. The greater the possible return, the higher the level of risk (probability of failure) which can be taken. Several other criteria will be applied to the decision process. These include location (offshore/onshore, distance from facilities or export routes), tax regime of the relevant country and the characteristics of the operator (risk taker/ avoider, cash rich, etc).
According to information from the text, choose the correct answer.
1. Which geological conditions are important for drilling?
a. properties of rocks and mapping;
b. reservoir, top seal, trap, source rock;
c. outcrops, well data, seismic data, scout data.
2. Which data are necessary for reservoir description?
a. well data, seismic data, geological surveys, scout data;
b. only well and seismic data;
c. only well data and geological surveys.
3. A trap
a. is older than the maturity age of a source rock;
b. contains the porous and permeable rocks;
c. contains only source rocks.
4. What are the play maps made for?
a. to define specific leads;
b. not to do extra work;
c. to get a license.
5.The term “reservoir” means
a. tank;
b.lake;
c. basin.
6. The term “petroleum play” means
a. seismic data processing;
b. group of oil/gas fields;
c. reservoir exploration