Steps for executing a well test- The holy grail of well measurement part 2.2

Steps for executing a well test- The holy grail of well measurement part 2.2

October 18, 2019

As promised in the first part of this article, I will continue to describe the steps you should note when executing a well test and try to describe the perfect system for such a test. Let’s begin!

Well test process

With today’s existing procedures, companies follow a workflow process that can be more manual or automatic, depending on the company.

The steps for the current methodology are approximate as follows:

1.Scheduling the well test

Well tests are scheduled according to the different level of needs. The well to be tested must be identified, on which well test resource (tank, three-phase separator, multiphase, etc.) and at which moment. A list of wells to be tested is created with their priorities. A set of logical rules is used to determine the priority of the well that will follow in the sequence: The time elapsed since the last well test, the production of the well, whether the well recently had operational problems or is in abnormal operation, well with recent work on downhole or surface, etc. This list is then reviewed and approved.

2.Preparing the test

Once the well to be tested over a given test resource that has been selected, the preparation stage allows you to configure the basic parameters that the system needs to carry out the testing of that well. Again, depending on the company, the system may be more or less automatic. Configuration of well test mode (continuous, batch or semi-continuous), automatic configuration of the well test tuning loops for the well to be tested according to the testing mode, chromatography load, salinity, historical well test, purge time, testing time, etc. These are some of the parameters, among many others, for the individual preparation of each well to be tested. These parameters are transmitted to the local PLC/DCS (if they exist) so that it can begin to carry out the activities of the well test.

3.Executing and Controlling the test

Once the well has been programmed and prepared to be tested, the well test itself is carried out using the system and instrumentation selected for each case. Depending on the infrastructure of processes (well test resource), instrumentation, control, and communications, the test can be fully automatic or have tasks that must be performed manually.

The primary measurement and the duration of the testing, as well as the calculation of the total flow (total liquids, gas and water cut-off),  are generally carried out in a PLC or DCS of the plant.

This PLC/DCS must contain the logic to determine the stable flow condition. For this, the PLC/DCS starts the testing after waiting a purge time that is different for each well. The purge time is the average time of displacement required by the fluid from the well to the test resources that are aligned for the test plus the time needed by the fluid to displace the fluid from the previous well and put the well test resource in the regime.

In a fully automated operation, the well test system executes the well test logic according to the preparation (continuous, batch or semi-continuous), computes and historically stores the different variables for each fluid. During the testing of a well, the possible well test states will be minimally the following: Well in purge, beginning of well test, test in execution, test in stop, test finishing, storing results, etc.

With adequate well test resources and fully automated, the accuracy obtained will be maximum and the duration of the well test will be the minimum and at the same time, we increase well test frequency.

4.Visualize, analyze, use and share the results

During the progress of the well test and once it is finished, the results should be sent to a database where they will be stored historically. Finally, the well test results are stored, all the history of execution of the test, its parameters, the qualification of the test and all parameters that have been relevant during the execution.

The resulting information is also relevant for the improvement of subsequent well tests of the same well, being able to reuse the information. These results are a source of information for the generation of management reports, key indicators and assistance in making strategic decisions. This database is a source of queries for the entire organization. From here, valid test results are sent to the production management system to be used in production accounting.

Normally this workflow process is integrated with other components and systems such as well telemetry, production management system, maintenance system, etc.

What are the variables that we can improve in the current processes?

Considering the importance of the information provided by a well test, it is highly desirable to increase both the frequency and accuracy of measurements. Nevertheless, perhaps we should think outside the box, and not think about the well test processes as they are today, which require measuring with some frequency per well. It would be ideal to measure continuously and more economically. The process explained above could change radically.

What would be the ideal system?

– A completely “rangeable” equipment or system. We can reach to test any of the wells and conditions that we have in our oilfields.

– That can measure continuously and accurately (no need to measure downtime of the well).

– That is economical enough so that it can be placed in many low production wells.

– A system that allows well tests to be performed in an organized manner.

– To reduce the number of surface installations required

– Improve measurement accuracy

– With results of greater reliability to the results

– Achieve an automated and supervised operation of the entire well test process

This is the “holy grail”, the system that all companies are looking for, but today is only a myth at least for the conditions mentioned above.

So… what can we do?

Many things can be done to approach something like the Holy Grail, and the companies are working mainly on these three lines:

– Measuring equipment becoming more and more rangeable.

Management systems that optimize the measurement process.

– Data science applied to well test

Every day we get closer to the Holy Grail, as technology improves with more precise and faster measurements. However, I still believe the answer is outside the box. We should stop thinking about the current work procedures, break these paradigms and concentrate on the final objectives to find new technologies and new work processes. Without a doubt, this would be a huge change for the oil & gas industry, since the oil and gas industry has been doing well testing the same way, or almost the same way, for decades. In the next article, I will try to analyze the reason for this.


Picture credits: vesnafoto- stock.adobe.com

2 Comments so far

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  1. Egejuru martins
    #1 Egejuru martins 13 November, 2019, 13:14

    What type of portable equipment is used in well testing at the wellhead not at the production facility ?

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  2. Gustavo Cerezo
    #2 Gustavo Cerezo 19 November, 2019, 14:18

    There are a variety of systems for measuring at the wellhead, and everything will depend on the type of well (oil flow, gas, water, whether it has sand, etc. and other variables). Today there is no single solution to measure in a single and no so expensive way in the wellhead, and in a continuous way, so I dare to call it the holy grail.
    The use of two-phase or three-phase mobile separators is very widespread, which can be used at the wellhead or in a collector of wells. Yokogawa has several technologies for instrumentation and automation of mobile test separators. If the well is only a gas producer, or only an oil producer, simple meters, such as Rotamass, can be used. If it is an oil producer, but have some presence of gas (in bags, or associated gas) can also be used Rotamass technology that can measure oil with the presence of gas. Also of course with the presence of water. There is no single answer, each case must be analyzed. .

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