Drillstem Test or DST

Test Your Knowledge

Drillstem Tests (DSTs) Quiz

Instructions: Choose the best answer for each question.

1. What is the primary purpose of a Drillstem Test (DST)? a) To permanently extract oil and gas from a well. b) To collect information about a potential reservoir while drilling. c) To measure the depth of a well. d) To stimulate oil and gas production in a well.

2. How are reservoir fluids isolated during a DST? a) Using a specialized drilling bit. b) By injecting a high-pressure fluid. c) By using downhole packers and valves. d) By temporarily stopping the drilling operation.

3. Which of the following is NOT a benefit of conducting a DST? a) Early reservoir evaluation. b) Cost-effective assessment. c) Reduced risk of production problems. d) Eliminating the need for further exploration.

4. What type of data is collected during a DST? a) Only pressure data. b) Only fluid samples. c) Pressure, flow rate, and fluid samples. d) Only wellbore temperature data.

5. DST data helps in: a) Determining the best drilling trajectory. b) Designing well completions to optimize production. c) Predicting the exact amount of oil and gas in a reservoir. d) Eliminating the need for further production testing.

Drillstem Tests (DSTs) Exercise

Scenario:

A newly discovered reservoir is being evaluated using a Drillstem Test. The following data is collected:

• Reservoir Pressure: 2500 psi
• Production Rate: 100 barrels of oil per day
• Fluid Samples: Show a high oil content and low water content.

Task:

Based on the provided data, what conclusions can you draw about the reservoir and what implications might this have for future development?

Techniques

Chapter 1: Techniques

Drillstem Test (DST) Techniques: A Comprehensive Overview

This chapter delves into the various techniques used to execute a DST, explaining the intricacies of equipment, procedures, and the importance of meticulous execution for reliable results.

1.1 DST Equipment:

• Packers: These are essential components for isolating the target zone. They come in different types, including mechanical packers, inflatable packers, and hydraulic packers, each suited for specific well conditions.
• Downhole Valves: These valves control the flow of reservoir fluids into the drill pipe chamber. Various valve configurations exist, including single-point valves, multi-point valves, and variable-choke valves, offering flexibility in controlling production rates.
• Pressure Gauges: Accurate pressure measurement is crucial for DST analysis. Modern DST tools incorporate high-precision pressure gauges, capable of capturing fluctuations in pressure throughout the test.
• Fluid Sampling Equipment: Specialized equipment is used to collect samples of the produced fluids. This can include downhole sampling vessels, separators, and filtration systems, ensuring accurate representation of the reservoir fluid composition.
• Wireline Tools: These tools are used to deploy, retrieve, and monitor DST equipment. They are crucial for accessing and manipulating components within the wellbore.

1.2 DST Procedures:

• Setting the Packers: Packers are carefully placed in the wellbore, sealing off the target zone from the surrounding formations. The choice of packer type and placement depends on wellbore conditions, reservoir pressure, and the desired test objectives.
• Pressure Build-Up: Once the packers are set, pressure is allowed to build in the isolated zone, allowing for pressure drawdown studies and analysis of reservoir fluid properties.
• Fluid Production: The downhole valve is opened, enabling reservoir fluids to flow into the drill pipe chamber. Production rates are carefully monitored and recorded using surface flow meters and pressure gauges.
• Data Acquisition and Analysis: Pressure and flow rate data are continuously recorded throughout the test, providing insights into reservoir behavior. Samples of the produced fluids are collected and analyzed to understand their composition and properties.
• DST Completion and Retrieval: After the desired test duration, the valve is closed, and the packers are retrieved. The gathered data are then analyzed, and decisions are made regarding well completion design and future production strategies.

1.3 Importance of Accurate Execution:

DSTs are highly sensitive procedures requiring meticulous execution to ensure reliable results. Factors impacting the accuracy of DSTs include:

• Equipment Calibration and Maintenance: Proper calibration and regular maintenance of equipment are crucial for accurate pressure and flow rate measurements.
• Proper Packers Placement and Sealing: Ensuring that packers are correctly placed and effectively seal off the target zone is essential for accurate reservoir pressure and fluid production data.
• Accurate Data Acquisition and Analysis: Reliable data acquisition and thorough analysis are crucial for interpreting the results and drawing meaningful conclusions about the reservoir's characteristics.

1.4 DST Variations:

Different DST variations are used in the field to address specific well conditions or objectives. These variations include:

• Single-Point DST: A single-point DST is used to assess the productivity of a single zone within the wellbore.
• Multi-Point DST: Multiple points within the wellbore are isolated and tested independently to evaluate the productivity of different zones.
• Flowback DST: This variation is used to measure the flowback of formation fluids after acidizing or stimulation treatments, evaluating the effectiveness of the treatment.

Conclusion:

Understanding the various DST techniques, equipment, and procedures is crucial for conducting successful tests and obtaining reliable data. This chapter provided a comprehensive overview of the techniques employed in DSTs, highlighting the importance of accurate execution and meticulous data analysis for extracting valuable insights from these complex procedures.