RFT vs MDT vs DST

RFT Repeat Formation Tester can take an unlimited number of formation pressure measurements and up to two fluid samples in a single trip in open hole. Two sample chambers are available in the tool to take samples from two different zones, or to take a segregated sample from one zone Two pretest chambers of 10 cc each are automatically opened after the tool is set to withdraw 20 cc of fluid at two different rates. The pretest samples are not saved. Pressure drawdown during this period and the following build-up curve are recorded at the surface and provide data for formation pressure and permeability calculations. The formation fluid is made to enter a chamber (first pre-test chamber) through a special valve that limits the flow rate to about 60 cm3/min. The sampling pressure is measured. When the first chamber is full, it is closed-off and a second pretest chamber is filled at a higher rate (150 cm3/min), while measuring the fluid pressure.

It may be decided that the tool should not take an operational sample, but move on to another depth. If this is the case, the pretest chambers are emptied into the borehole, the back-shoe is retracted, the drilling mud pressure is re-recorded, and the tool moves on to another depth. If an operational sample is required, one of two valves to two chambers is opened so that fluid flows into a chamber. The fluid sample is commonly 10 liters.

The most common problems are: A Tight Test. If the sample is very impermeable the sampling pressure drops to near zero. In this case it will take too long to obtain a pressure reading and the tool may stick in the borehole. Stuck Tool. Usually when the tool has been set at a given depth for some time. Plugging. Reservoir grains from the formation may enter the tool and block the flow lines, especially in unconsolidated samples. This problem is reduced by the filter in the sampling probe, but fine grains may still get through. Seal Failure. If the packer fails, the drilling mud will be sampled and the mud pressure will be recorded.

Log Quality Control: 1) Depth Matching 2) Hydrostatic Pressure (HP) Before and After 3) Mud Density Calculation and Comparison 4) Formation Pressure Buildup Data QA and QC  Strain Gauges: Wellsite Calibration & Verification  Quartz Gauges: Factory Calibrated

MDT The available modules are as follows: MRPC Electrical Power Cartridge. This module converts AC power from the surface to provide DC power for all other modules in the configuration and can only be connected at the top of the string. MRHY Hydraulic Power Module. This module contains an electric motor and hydraulic pump to provide hydraulic power for setting and retracting the probe modules. It can be placed almost anywhere in the tool string, but must be adjacent to the probe module that it is powering. MRPS Single Probe Module. This module contains the probe assembly with packer and telescoping back-up pistons. It also houses the pressure gauges, fluid resistivity and temperature sensors and the pre-test facility. It can be placed anywhere in the string, but must be connected directly to the hydraulic power module. There are two versions of the MRPS, one with strain gauge only and one with both strain and quartz gauges. MRSC Conventional Sample Chamber Modules. These are available in three sizes: 1, 2-¾ and 6 gallons. The 1 and 2-¾ gallon chambers exist in both H2S and non-H2S versions. The 1 and 2-¾ gallon chambers can be placed anywhere in the string; however, the 6 gallon chamber can only be placed at the bottom since it does not have a flowline or electrical bus. The 6 gallon chamber can be expanded in volume in multiples of 6 gallons by adding more sample cylinders. MRMS Multi-Sample Module. The MRMS contains 6 sample bottles of 450 cc each. The bottles are not part of the MRMS asset. In fact, they must be ordered separately as MPSR-AB. This module allows one to collect up to 6 samples for PVT (Pressure Volume Temperature) analysis per trip downhole MRPO Pumpout Module. This module allows you to pump reservoir fluid to the borehole so that virgin fluid can be recovered. The module can also be used to pump fluid from the borehole into the flowline for inflating the packers of the dual packer module. There is a facility which allows the module to pump within the flowline (e.g. from a sample chamber to the inflatable packers). MRFA Optical Fluid Analyzer Module. This module uses optical techniques to detect the presence of oil, water and gas in the flowline. Visible and near infra-red

spectroscopy allows it to distinguish between oil and water while reflection techniques allow gas detection. MRPD Dual-Probe Module. This module contains two probes mounted diametrically opposite each other. It is connected below a single probe module to form a multiprobe system. This system is used to make anisotropic permeability measurements. A large volume pretest with known flowrate is necessary to create large enough pulses in the formation. For this reason the flow control module is used in conjunction with the multi-probe system. Two versions of MRPD exist, one with strain gauge only at the "horizontal" probe and one with both a quartz gauge and a strain gauge at the "horizontal" probe. MRCF Flow Control Module. This module contains a 1 liter pretest chamber where the flowrate can be accurately measured and controlled. It can be used to create a large enough pressure pulse in the formation for multiprobe measurements. The MRCF can also be used in conjunction with the MRMS as a 1-liter receiver for the MRMS water cushions. This allows sampling at an accurately controlled flowrate or drawdown. However, note that the MRCF cannot be used as an additional sample chamber for the purpose of bringing fluid to the surface. MRPA Dual Packer Module. Two inflatable packers are mounted on this module. When inflated, they isolate an area of borehole wall about two thousand times the area of a conventional probe. This allows a large volume drawdown at high flowrate followed by a build up test to estimate permeability further into the reservoir (50 to 80 feet). There are two versions of the MRPA available, one with a strain gauge only and one with both strain and quartz gauges.

MDT has a bussed flowline which means the flowline passes through each module except MRPC & MRSC-EB (6 gallon).

RFT vs MDT Feature

RFT

MDT

Pretest volume

20 cc fixed

0-20 cc variable

Pretest rate

Two fixed rates

Variable

No control

Programmable

Avoid going below bubble point. Improved perm calculation.

HP 0.01 % reading +2 psi

CQG 0.01 % reading + 2 psi.

No comparative MDT advantage.

HP 0.01 psi.

CQG 0.01 psi

No comparative MDT advantage.

HP. Within 1 psi. in 10 minutes

CQG. Within 1 psi in a few sec. with dynamic correction 2 min. without dynamic correction.

Faster pressure measurements. Up to 50% time savings per pretest. More evident in low-medium perm. RIG TIME SAVINGS

HP 0-12,000 psi.

CQG 0-15,000 psi

Samples per trip

2 samples maximum. i.e. one segregated sample per trip.

Fluid resistivity Sensor

None

12 MRMS samples plus additional sample chambers. Resistivity cell in flowline. (0-20) ohmm with .01 ohm-m resolution. From 6.0 to 14 in. without dressing the tool.

Pretest drawdown pressure Quartz gauge accuracy Quartz gauge resolution Quartz gauge dynamic response: Response to 5000 psi shock. Quartz gauge pressure range

Tool hole size dynamic range.

Large hole kit

From 6.0 to 9.0 in. without dressing the tool Many spacer kits available but minimum hole size also reduced.

Mechanical Strength

N/A

Cased hole usage

Kit Available

Large hole kit works in 8.5 to 19.0 in. holes 160,000 lbs in tensile mode. 166,000 lbs at 10,000 psi and 240 °F Cannot be used in cased hole.

Comparative MDT Benefit Faster pretest in low and medium permeability. RIG TIME SAVINGS Drawdown rate adapted to formation perm. Avoid excessive drawdown and going below bubble point. Improved perm calculation.

Pressure measurement possible in deeper high pressure wells. Reduced operating time due to less runs in the hole for more than two samples per trip. RIG TIME SAVINGS. In situ Rw estimate. Real time decision making during sampling saves time and improves chamber utilization. Increased probability to make measurements in washed out holes even below tight restrictions. Gets data where RFT cannot. Gets data where RFT cannot. More rugged for TLC operations. Less risk of damage during fishing. Data available in 6.0 in hole with TLC. Not possible with RFT on TLC. No comparative MDT benefit.

MDT vs DST MDT

DST

Gets the reservoir pressure point by point

Just 3 point pressure measurement

Investigates near wellbore regime

Much more deeper in reservoir

Takes time just as a trip

Takes time for days

No flow to surface so there is no need for flare or disposal system Doesn’t evaluate the reservoir boundary & fault

Flow to surface Evaluates the reservoir boundary & fault

Evaluates the specific layer properties

Evaluates the whole reservoir

Specifies the depleted or thief zones

Doesn’t do that Measures 𝑃̅, well productivity, IPR curve, wellbore damage (S), reservoir boundaries & ̅ faults, drainage radius, 𝐾

Measures Pi, fluid gradient, fluid contacts, vertical homogeneity and heterogeneity, communications between layers