After drilling an appraisal well completed and gas or oil reserves proven, the oil and gas company must put a strategy to develop the field. Whether to develop the field by oneself or by finding a partner is among items in the company strategy. Having the strategy in hand, development team prepares the development proposal.
A GGR study (Geology, Geophysics, Reservoir study) to conclude the reserve is conducted in-house or by giving it to a third party. Some oil and gas companies have reservoir simulator to numerically evaluate reservoir and forecast the gas / oil production and recovery. The production facility will be sized according to the number of wells going to drill and the production rate. The capital expenditure and operating cost along with risks are put into economic analysis.
After the management approves the development proposal, operation teams implement it in the field. Drilling department designs and drills wells. The production department builds the production facilities. Engineers evaluate day-to-day well performance, collecting data, and aim to reach production targets in the development proposal.
The process can be explained by diagram in Figure 1. The processes are repeated until no additional alternate mechanism to continue exploiting the reservoir.
The data which are categorized into two are high rate and low rate data. High rate data are such as production rate, injection rate, wellhead pressure, downhole pressure, downhole temperature, and oil/gas composition. If necessary, low rate data such as 4D seismic and cross well electrical measurement can be acquired based on evaluation results. Both data are handled differently.
In evaluating processes, numerical and analytical models are done separately even they use the same logs, core samples, production data, and fluid samples. A history match is run to establish constraints. Volumetric volume is compared to material balance volume and then concludes whether these volumes are consistent. If there were inconsistencies, the inconsistency would be put in risk factors for economic analysis.
Some companies do not have software to perform numerical analysis to do reservoir modeling for the oil and gas reservoir. Instead, the companies can do an analytical model in-house by mapping peak well rates and total well recovery. Decline rate evaluation also can be done to predict opportunities in wells.
After doing the evaluation, the current production compares to production target in the development plan. If the production target was not reached, the development plans were adjusted including the size of the projects, reservoir development plans, etc. On the other hand, if the production target was reached, the development plans were not adjusted instead the project was continued including day-to-day operational plans.