Well test

WELL TEST.

In the Petroleum Industry, a well test is the execution of a set of planned data acquisition activities to broaden the knowledge and understanding of hydrocarbons properties and characteristics of the underground reservoir where hydrocarbon are trapped. The test will also provide information about the state of the particular well used to collect data. The overall objective is identifying the reservoir's capacity to produce hydrocarbons, such as oil, natural gas and condensate.
Well test are various ways to categorize test types by its objectives, however two main categories only by objectives, these are productivity tests and descriptive tests. According to The Lease Pumper’s Handbook of Oklahoma Commission on Marginally Producing Oil and Gas Wells, there are four basic well test types: potential tests, daily tests, productivity tests, and gas oil ratio tests, the latter three in the broader productivity test category.

Information from Well Test

Data gathered during the test period includes volumetric flow rate and pressure observed in the selected well. Outcomes of a well test, for instance flow rate data and gas oil ratio data, may support the well allocation process for an ongoing production phase, while other data about the reservoir capabilities will support reservoir management.
Test objectives will change throughout the different phases of a reservoir or oil field, from the exploration phase of wildcat and appraisal wells, through the field development phase and finally through the production phase, which may also have variations from the initial period of production to improved recovery by the end of the field lifecycle time.
Professionals working with reservoir modeling may get information about the rock permeability from core samples. Other sources of information to the model are well log data and seismic data, but such data are complementary only, and for example, seismic data is insufficient to interpret whether a structural trap has been sealed. Information from well tests will supplement the amount of information with flow rate data, pressure data, and other, which is needed to build a rich reservoir model.
Most well tests consist of changing the rate, and observing the change in pressure caused by this change in rate. To perform a well test successfully one must be able to measure the time, the rate, the pressure, and control the rate. Well tests, if properly designed, can be used to estimate the following parameters.
§  Flow conductance
§  Skin factor
§  Non-Darcy coefficient (multirate tests)
§  Storativity
§  wFractured reservoir parameters
§  Fractured well parameters
§  Drainage area
§  Distance to faults
§  Drainage shape

Purpose

Exploration wells

§  Fluid sampling (Primary reason)
§  Measuring the initial pressure
§  Estimating a minimum reservoir volume
§  Evaluating the well permeability and skin effect
§  Identifying heterogeneities and boundaries. 

Producing wells

§  Verifying permeability and skin effect
§  Identifying fluid behavior
§  Estimating the average reservoir pressure
§  Confirming heterogeneities and boundaries
§  Assessing hydraulic connectivity.

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