Pressure/volume/temperature (PVT) properties help determine the estimation of reservoir reserves and help predict reservoir performance and economics. Conventional PVT analysis can delay the decision-making process from weeks to months depending upon the logistics involved in transporting a sample from its acquired location to a PVT laboratory. Therefore, the sooner this information can be provided, the faster you can make the critical decisions regarding your reservoir.
Pressure testing in an LWD environment can provide safety and drilling optimization as well as control overbalance and equivalent circulating density (ECD). Representative fluid samples provide information on production potential of the reservoir, design and development of production facilities, and completion and development costs. Before the capture and retrieval of fluid samples we must identify in real time what fluid is being pumped through the tool. The FASTrak service sensors identify real-time density, viscosity, refractive index, and sound speed measurements to provide real-time fluid typing and cleanup monitoring.
Proven track record of data delivery in an LWD environment
Acquiring samples with less than 2% contamination, the FASTrak service has been used worldwide—in a variety of operating environments and well types—to acquire oil, gas, and water samples in both oil- and water-based muds (OBM and WBM) in different formations such as sandstones and carbonates with permeability levels ranging from 0.2 mD to 5 D.
The FASTrak service has set world records for both sampling and pressure testing, including an operation in Vietnam during which more than 150 pressure tests were done in a single run, and an Australian operation during which 14 gas samples were recovered in a single run and 26 samples in two runs.
Service description
The FASTrak service consists of four main sections. The power module provides the tool with the power necessary to extend and retract the sealing element, open and close valves within the tool, power the fluid identification sensors, and provide power to the drawdown pump.
The pump and analyzer section is the heart of the tool. Within it is the sealing element, quartz pressure gauge, fluid analyzer, drawdown pump, and sample pressure gauge.
The tank module is capable of carrying up to four tanks. If required, four tank modules can be connected in series, giving the FASTrak service the capability of retrieving up to 16 single-phase fluid samples in a single run. The termination sub provides an exit to the wellbore for the contaminated fluids while the system is cleaning up virgin formation fluid.
Advantages of electromechanical systems
The tool incorporates an electromechanically driven drawdown pump that enables a nearly autonomous operation to maintain fluid phase integrity. Automation delivers the most complete set of fluid property data in real time for efficient decision making. It enables the operator to monitor the fluid identification trend carefully and in real time, even from remote locations.
Integrated answers while drilling
The FASTrak service is designed for full integration with other Baker Hughes drilling and formation evaluation services, including the MagTrak? LWD magnetic resonance service, to qualitatively verify permeability and viscosity measurements. In addition, Baker Hughes offers 24/7 access to reservoir engineering experts for real-time interpretation and advice, both onsite and around the world via the Baker Hughes WellLink? RT Internet data transmission service and a network of worldwide collaboration centers.
Measurements of fluid density, viscosity, sound speed, and continuous refractive index are made downhole under reservoir temperature and pressure conditions. By monitoring these responses with the FASTrak service, reservoir fluid samples can be collected with minimal contamination while providing PVT and downhole fluids information.
At the core of the FASTrak service’s real-time fluid analysis are four sensors: the piezoelectric tuning fork, the acoustic transducer, the temperature sensor, and the refractometer. The latter of which is highly sensitive to changes in water salinity.
Since downhole fluids have different refractive index values of we can differentiate the distinct fluids with this methodology. Density and viscosity are measured by observing the resonant frequency response of a sensor immersed in a fluid at a particular pressure and temperature. Sound speed measurements are achieved by an acoustic transducer linked directly to the flow tube of the tool that measures the response of the acoustic travel time across the fluid.
An additional benefit is that by using a very high frequency transducer, the resultant resolution is very high, which means very small changes in contamination can be detected.
Changes in salinity can also be detected during formation water sampling in a water-based environment, allowing differentiation between the filtrate and formation water. With a given fluid temperature, pressure, and real-time oil density, the sound speed is highly correlated to the gas/oil ratio. Compressibility is also calculated from fluid density and sound speed.
CASE HISTORY
An operator in the Gulf of Mexico required high-purity fluid samples for accurate reservoir characterization. Due to the risk of differential sticking in the 45° well, a time limitation of 2 hours per station was imposed during the sampling operation.
The FASTrak service was combined with the Baker Hughes LithoTrak? Advanced LWD porosity service, OnTrak? integrated measurement while drilling/LWD service, and AutoTrak? G3 rotary steerable drilling system to address the operator’s challenges. Five zones of interest were identified using the formation evaluation suite.
Seventeen pressure tests were successfully taken, with mobilities ranging from 2.0 to 770.0 mD/cP, that identified several oil and water gradients. In combination with the pressure testing operation, the FASTrak service successfully captured five single-phase samples. The Baker Hughes SmartPad? intelligent control system, which efficiently seals even in highly unconsolidated sand formations and irregular boreholes, was crucial to the 100% sealing success during the pressure testing, pumpout, and sampling operations.
Based on the real-time fluid analysis data, one water sample and five oil samples were recovered successfully in different zones of the reservoir with an average time on the wall of 90 min. PVT results showed OBM sample contamination rates as low as 2%. The high purity of these samples is comparable to samples captured using focused fluid sampling wireline technologies. A comparison of the downhole fluid analysis data from the FASTrak service and the PVT laboratory showed that density values were within 5% and gas/oil ratio varied up to 10%.
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