This article assumes you are familiar with openhole (wireline) logging and the Schlumberger Modular Dynamic Tester (MDT) tool.
How do you plan an MDT mega-combo sampling job on a gas well? First of all, we must clearly understand our requirements as an interested party.
Typical questions we would ask are:
1. How many sampling points are planned?
2. How many samples will be taken per point, ie how many sample bottles or chambers?
3. Are the samples for PVT and/or H2S analysis?
4. Would SPMC and/or MPSR be required?
5. Are water samples required (in wells with a stretch of water below the hydrocarbon)?
6. Is well site transfer and analysis required?
Most sampling is now done using the low-impact sampling method, but it’s worth asking. These questions will help determine the MDT modules to run in the well.
The decision-making process regarding when to take a sample should also be clearly defined. The decision is usually made by the company representative in consultation with the service company’s reservoir expert/engineer.
The MDT toolchain consists of several different modules, each designed for specific purposes. Each module added to the suite of tools must be selected to meet the goal of obtaining PVT-quality samples. The modules for analyzing gas quality are the CGA (Condensate-Gas Analyzer) and the LFA (Live Fluid Analyzer). Also to pump formation gas, the MRPO (MDT Reservoir Pump-out) is required. The service company will specify other modules required as standard to operate the MDT tool. SPMC (Single Phase Multi-Sample Chamber) and MPSRS (Multi-Phase Sample Receiver) are sample bottles (250 cc and 450 cc respectively) typically used to sample PVT grade gas. When well site transfers and testing (SPMC) are required, the utility company should be notified so that the necessary equipment can be mobilized to the well site.
Pipeline MDT sampling jobs can take more than 2 days, so utility staff should be prepared for 24-hour coverage.
Additional considerations not covered in this article include equipment specification for compact tanks. This covers the type of probe to be used and even the use of dual packers. This is a summary of planning for a pipelined MDT sampling operation, further information should be obtained from internal experts such as the operations petrophysicist, service company or consultants (cable witnesses).
