Introduction on Production Well Testing in Upstream Oil & Gas Measurement and Allocation

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Why Well Test ?

Reasons for Production Well Testing:

  • Regulatory/Statutory Requirements
  • Economics
  • Reservoir Management
  • Production Management

Application of production well test data :

  • For calculating production well test volumes and rates.
  • For use in measurement and back allocation.
  • For validation and update of well flow models and virtual flow metering

What? – Basic theory of Production Well Test

After well drilling is completed and equipped with sub-surface and surface facilities, the next activity is production well testing to find out the production flowrate of the well. Well testing is also carried out on old oil wells that are still in production to find out whether it is still efficient and effective for production, and what factors will arise, as well as steps that must be done in shortterm or longterm so that wells can successfully produce fluid.

Measurement of the results of well can be done by measuring the production output of thus well at the Collection Station or Tank.

The work activity of measuring the production of a well is called: Well Testing.

The well itself is called: Well under test, which is a well that is being appealed.

  • Well test (uji sumur) is one of the methods in petroleum engineering that is carried out to determine the causes of problems that occur in the wellbore, both oil reservoirs and gas reservoirs
  • The main purpose of a well test is to determine the ability of a formation to produce.
  • If the tests are carried out good and then the results are analyzed properly, a lot of very valuable information is obtained, such as effective fluid permeability, formation damage or repair around the wellbore due to drilling or during production, reservoir pressure, reservoir boundaries and drainage radius .

Picture5

Figure 1—Well Rate Determination Tree

Shown in Figure-1 above – is a well rate determination tree that summarizes the various methods for ascertaining well production rates and outlines the necessary equipment, techniques, and application.

 

Well Testing Methods

In this document, well testing is a well production testing job to find out production data from each well (oil, water and gas) per day. This data is important for Petroleum Engineers to analyze well and formation as a whole, whether the well is still producing good or requires a well service or workover job to maintain / increase the rate of production.

Well testing is carried out with 2 (two) methods, namely:

1) Manual Well Testing (MWT)

2) Automatic Well Testing (AWT)

 

Well Test – Requirements ?

Production well testing requirements are often cited in regulatory permits, commercial agreements, and operator’s policies. This can include test frequency and duration, and the use of the production well test measurement in well rate determination scenarios and/or allocations. The application of this document shall be in conformance with all applicable regulations, permits, and agreements.

All production well test requirements outlined in regulations, permits, or agreements shall be documented.

 

How? – Conducting a Production Well Test

Steps of Well Test :

  • Preparation,
  • Initiation and measurement,
  • Validation, and

Volume and rate calculations for separator, multiphase flow meter, and tank production well test systems

 

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Figure 6—Production Well Test Initiation and Measurement Workflow (API MPMS Chapter 20.5)

 

Controlled Operational Conditions Validation

It is important that the production well test is validated as representing a measurement of gas, oil, and water from a single well during a specified length of time under controlled operational conditions. The operator should establish and document acceptance criteria for controlled operational conditions validation. The following list provides suggested acceptance criteria parameters for inclusion in controlled operational conditions validation of a production well test:

—   well isolation in the production well test system for the duration of the purge, flow pre-stabilization, and production well test measurement period;

—   purge times (volumes) sufficient to ensure representative single well flow at the measurement point;

—   demonstrated well flow stability for the duration of the production well test:

—   wellhead and/or bottomhole pressure relatively constant and within ±5 % of normal operating conditions,

—   wellhead and/or bottomhole temperature relatively constant and within ±5 % of normal operating conditions,

—   flow rate variation within ±5 % for each phase being tested,

—   watercut variation within ±5 %,

—   measured GOR variation within ±5 %,

—   minimum of 4 hours of stable flow.

—   fluid measurement obtained within the operating envelope of the measurement system;

—   no changes to equipment (e.g. chokes settings, artificial lift settings, chemical injections) for the duration of the production well test.

 

Production Well Test Measurement Uncertainty

 

Measurement in upstream production has a much higher level of uncertainty when compared to measurement at custody transfer conditions. For production well testing, oil is saturated with gas at production pressures and temperatures. Gas is saturated with hydrocarbon and water, and might include entrained liquids. Additionally, oil and water emulsions might be present. It is recognized that these conditions result in the elevated uncertainties relative to custody transfer, where treated gas and de-watered oil pumped from tmospheric tanks are measured.

Owing to the challenges of measurement in an upstream production environment, and the potential complexities of a production well test system, uncertainties associated with the individual phase (i.e. gas, oil, water) measurement results can range from as low as ±2 % to as high as ±10 % or greater. It is not the intent of this document to specify an uncertainty range acceptable for production well testing. However, the operator should evaluate the importance of the data and assign an acceptable tolerance on uncertainty accordingly.

 

Terms and Definition

  • Allocation – The mathematical process of determining the proportion of produced fluids from individual entities (zones, wells, fields, leases, or producing units) when compared to the total production from the entire system (reservoir, production system, and gathering systems) in order to determine value or ownership to attribute to each entity. (API MPMS Clause 3.1.2)
  • Production Well Test
    • The measurement of gas, oil, and water quantities from a single well during a specified length of time under controlled operational conditions. (API MPMS 20.5 Clause 3.1.16)
    • Well Test (Uji Produksi sumur) adalah Pengukuran kemampuan produksi Reservoir. (PTK-062 Bab-I Pasal 5 Sub-pasal 5.53)

References:

Standard Best Practise:

Applicable Standards/Code/Regulationa/Best Practices in upstream oil & gas industry should be referenced for and will be used as the main basis for developing and implementing the Well Test Management, as below:

American Petroleum Institute (API) – Manual of Petroleum Measurement Standards (MPMS):

  • Chapter 20.1—Allocation Measurement;
  • Chapter 20.2—Production Allocation Measurement Using Single-phase Devices;
  • Chapter 20.3—Measurement of Multiphase Flow;
  • Chapter 5Recommended Practice for Application of Production Well Testing in Measurement and Allocation;
  • Chapter 8.1, Standard Practice for Manual Sampling of Petroleum and Petroleum Products
  • Chapter 11.1, Temperature and Pressure Volume Correction Factors
  • API MPMS 5.3 : Metering Measurement of Liquid Hydrocarbon by Turbine Meters, Includes Addendum 1
  • API MPMS 14.3.1 : Manual of Petroleum Measurement Standards Chapter 14 Concentric, Square-Edged Orifice Meters Parts 1 – General Equations and Uncertainty Guidelines

ISO/IEC:

  • ISO/IEC 17025 —General requirements for the competence of testing and calibration laboratories;
  • ISO/IEC GUIDE 98-3:2008 (EN) —Uncertainty of Measurement;
  • ISO 5167-1 : Measurement of fluid flow
  • ISO 9001:2015 Quality Management System – Requirements
    • Clause 7.2 Competence
    • Clause 7.5 Documented information
    • Clause 8.1 Operational planning and control
    • Clause 7.1.5 : Monitoring and measuring resources
  • Directive 017 Measurement Requirement for OG, Release date: November 21, 2018 : Directive 017 consolidates, clarifies, and updates Alberta Energy Regulator (AER) requirements for measurement points used for AER accounting and reporting purposes, as well as those measurement points required for upstream petroleum facilities and some downstream pipeline operations under existing regulations.
  • Measurement Guideline for Upstream Oil and Gas Operations, Version 2.0 : November 2018

Local Regulations:

  • Keputusan Menteri Tenaga Kerja Dan Transmigrasi Nomor : KEP. 250/MEN/V/2007 Tentang penetapan standar kompetensi kerja nasional indonesia sektor industri minyak dan gas bumi serta panas bumi sub sektor industri minyak dan gas bumi hulu bidang produksi sub bidang operasi produksi
  • PP no 2 th 1989 : standar nasional untuk satuan ukuran
  • PTK-062 Manajemen Operasi Produksi Minyak Dan Gas Bumi;
  • Pedoman Pelaksanaan Operasi Produksi dan Pelaporan Arus Minyak Dan Gas Bumi (PUPO-PPAM);

 

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