Estimation of Original Oil-in-Place in the Exploration Stage｜Asia Oceania
Oil and Gas Development Consulting and Engineering Company, Japan Oil Engineering

◆First of all, OIP estimation for the asset evaluation of oil and gas fields

The sufficient economical reserves of oil and gas are expected in order that the oil and gas fields become an exploration and development target as a commercial activity. Therefore, we calculate whether exists how much oil and gas in the mineral deposits underground through the reserves evaluation. Two of the calculation method of the deterministic approach and stochastic approach are used in the reserves estimation and the applicable calculation method at each stage of exploration and development will be different. Furthermore, the reserves evaluation is needed for the verification of the validity of the updated data in reservoir modeling work. In addition, reserves held by oil development companies, has been important from shareholders and investors as one of the index representing the corporate strength of the company. Therefore, the assessment of the precise reserves by the appropriate calculation method is the essential processes in terms of the success of projects related to oil exploration.

◆Evaluating 109 oil and gas reserves in the past 10 years

JOE has been carried out a reserves evaluation of oil and gas fields in the projects amounting to 109 in countries and regions for trading companies, banks, electric power companies and oil companies during the past 10 (2005-2015) years.

Exploration and development of gas fields are advanced actively through Australia from Indonesia in recent years. They are located in the exploration stage, because it has not yet been recognized as oil/gas field, which is equivalent to prospect. We will also introduce the outline about 1 case from them.

◆Estimation of original oil-in-place in the exploration stage

In order to evaluate a prospect located offshore in the northwest of Australia, virtual data room was open on the Internet. Grasping whole picture of the information, geologist and reservoir engineer visited the local physical data room and verify/evaluate the data directly.

Although in the mining area of interest a small number of drilling wells for the area, Prospect with the potential to be promoted to the oil and gas fields has been recognized multiple. In the evaluation of the Prospect of such exploration stage, we will focus also on the point of how petroleum system for oil and gas field deposits was established

Petroleum system is composed of following 3 elements 1) Existence of maturated source rock 2) Alteration/migration/accumulation processes 3) Trap system related to existence of matured source rocks. We revealed that existence of source rock and good chance of charge. With respect to number 2 we indicated that the carrier bed of sandstone spreads a wide range and many normal faults were developed associated with the rifting. And related to number 3 we investigate the reservoir rock, seal and trap preserving migrated hydrocarbon, and evaluated Probability of geological success (Psg) in each processes.

OIP was estimated by Monte Carlo simulation. Taking into account uncertainties suggested from the range of values in each of the input parameters, we determined the parameters in the volumetric calculation method. Finally, OIP was estimated that the mean value based on the probabilistic OIP was multiplied by the Probability of geological success (Psg).