Well Test -The holy grail of well measurement part 2.1

Well Test -The holy grail of well measurement part 2.1

October 17, 2019

Introduction

Well testing is a necessary practice in oilfields to determine flows of water, oil, and gas from wells.

Normally an oilfield has all types of oil wells with a great variety of flows of dry oil, water, and gas, as well as water cuts in a wide range, with the most diverse pressures, densities, salinities, presence of gas and types of oil. All these variables make testing a well accurately a complex problem.

What is a Well Test?

In Upstream, a well test is simply a period of time during which the production of a well is measured, either at the well head with portable well test equipment, or in a production facility. Nowadays well test measurement mechanisms are complex, expensive and not very accurate. This procedure is carried out tanks to separators (e.g. two-phase or three-phase, depending on the well).

At some companies, the testing measurement frequency is determined with a procedure, which prioritizes the wells with the highest production, those that have had an intervention, those that may have greater variations, etc. In companies with oilfields including a large number of wells, this frequency can be up to one test per well every one or two months. Sometimes there are minimal frequency requirements by state agencies. To conduct the necessary daily data for production management systems, the “downtime” of the well must also be accounted for. In order to have a better estimate of the well downtime, it is necessary to automate the measurement of each well. Depending on the lifting method (natural surge or artificial lifting systems such as mechanical pumping, ESP, PCP, plunger lift etc.), it will be the type of monitoring and control that each well must carry for the determination (among other things) of the downtime. However, we will talk about this in another article.

In this way, the “daily production” is calculated considering the downtime and the information from the most recent test of each well.

Purpose of a Well Test 

From a Production area point of view, the precise knowledge of this information makes it possible to determine the needs and limitations of the production stations and plants. As well as the determination of the mass balance by zones and the optimization of the movement of fluids, and the contrast with the fiscal measurements of the oil pipelines.

For the Resources area, the test is carried out in order to obtain information on the characteristics of wells and their evolution over time. This is important to know the state of the reservoir in general and to predict the behavior of the resources in the future.

In oilfields with a large number of low production wells, given the diversity and number of wells, there is no single mechanism to achieve these objectives. There is equipment that can measure very well the well in a continuous way within a range of flow, a range of water cut, without the presence of sands, etc. However, today, there is no single equipment that can measure oil, gas, and water simultaneously in all the ranges and characteristics that can occur in oilfields of this type.

Situation today

Well test current mechanisms are complex, expensive and not very accurate. The technologies on the market today for well testing are many and allow various configurations. From test tanks, three-phase or two-phase separators to multiphase meters, etc. However, most of these technologies are expensive, with variable range possibilities and can only measure “one well at a time”. According to the actual measurement process:

  • Current systems used for well test have a high CAPEX and OPEX.
  • Testing schedule is determined with inaccurate information.
  • Estimation of downtimes not accurate, or expensive to achieve.
  • Inaccuracies in well testing or well downtime result in non-localized losses.

In the second part of this article, I will explain the single steps that should be leveraged in order to receive correct and precise results for the well test.


Picture credits: Kovalenko I- stock.adobe.com 

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