Formation sampling-while-drilling (FSWD) technology has recently been introduced, and this new method of obtaining formation samples is expected to reduce costs in development and appraisal wells. Formation testing on wireline (FSWL) pumpout tools have become the preferred method for obtaining formation samples in the drilling stages of a well to appraise the production potential. Although FSWD has the potential of reducing the sampling time, many factors must be considered when evaluating the economic benefit of a new technology. Now that day rates for deepwater drilling have reached $1 million, this has become one of the primary considerations.This paper presents an economic model that can be used to evaluate the cost benefit and to make a comparison between wireline formation fluid samples acquired by the customer in a deep water field in Campos Basin, Brazil, in two scenarios (clastics and carbonates), with the simulation results obtained by the FSWD sensor.Recent publications indicate a potential to reduce the sampling time with FSWD because of reduced invasion time. They also consider other factors, such as the permeability, porosity, and in-situ viscosity of the producing intervals, and the mud system properties that can have an equal effect on the invasion and pumpout time required to reach a sufficiently low contamination sample to evaluate the reservoir.These factors are then used in an economic model that features operation costs for FSWL and FSWD, including the uncertainties regarding the following:• Fishing time, which is normally associated with the wireline operation • Reduced pumping times associated with lower invasion, which will also reduce operational pump failures associated with extending pumping times • Ability to obtain fluid samples in high angle or horizontal sections, reducing the operational time and enabling the operators to change their traditional well construction programs reducing or cancelling the need to drill a pilot well section and/or setting an intermediate casing string IntroductionWhen new technology is introduced to the industry, it can be very difficult to evaluate its potential economic benefit. The new technology has the potential to improve the quality and reduce the uncertainties of the information collected, or to obtain similar results at reduced costs. However, the risks and benefits are difficult to quantify. This is particularly true when evaluating similar technologies for wireline (WL) and logging-while-drilling (LWD). With the introduction of FSWD, which offers comparable benefits to FSWL, new methods must be developed to evaluate these technologies and to determine when it is of greater benefit to use the new FSWD rather than the well-established FSWL. This paper introduces a new economic value-added model that uses cost differences and considers the risks involved with its implementation. It is important to first understand the capabilities and potential benefits of FSWD.
Formation-testing-while-drilling (FTWD) technology was introduced in 2002 and has been used primarily for applications similar to wireline formation testers (WFT). These applications include accurate formation pressures, gradient analysis, formation connectivity, differential depletion, and flow barrier detections. A largely untapped application for FTWD is drilling optimization. The testing practices for drilling optimization are somewhat different than those used for typical WFT applications. In these cases, it is desirable to obtain pressures as soon as possible; and real-time test results are paramount. Combined with other downhole drilling information, such as vibration, torque, and weight-on-bit, drilling parameters can be adjusted to improve the rate of penetration (ROP) and make adjustments to the wellbore stability model in real-time. This paper reviews a Middle East case study in a carbonate gas reservoir. In part of this field, the reservoir pressure was uncertain due to possible communication with a high-pressure lower interval. Therefore, establishing the actual formation pressure was a priority. By monitoring the FTWD pressure tests in real-time, it was possible to verify the quality and validity of each test. Then, the test data was used to change mud parameters gradually. A composite log clearly indicates how decreasing annular pressures resulted in an increase in ROP. The method of testing and real-time monitoring results are reviewed and compared with high-resolution memory data from the FTWD tool. Comparison validated the real-time test data. Conclusions are drawn concerning drilling applications and how such test data can be utilized to improve the drilling process. Introduction The United Arab Emirates (UAE) has the fifth largest reserves of oil in the Middle East and is also an important oil producer. The Abu Dhabi Company for Onshore Oil Operations (ADCO) operates onshore and in shallow coastal water of the Emirate of Abu Dhabi. Abu Dhabi is also the center of the UAE oil and gas industry. The case study is a dual gas injector in a giant Cretaceous carbonate field in Abu Dhabi. The field is an elongated faulted anticline with a number of key uncertainties including the fault and fracture distribution and its impact on fluid flow in this large gas/condensate reservoir. The injector well was completed in upper Zone "1" and lower Zone "2" as shown in Fig. 1. In 2005, it was decided to plug back the original hole, side track, and re-complete the well as a single horizontal upper Zone "1" injector. Possible communication with Zone "2" required the drilling program to use higher mud weights to assure pressure control and well bore stability. Because of uncertainty in estimating pore pressure in Zone "1", a FTWD tool was planned to be utilized while drilling the 6-in. diameter horizontal section. The drilling plan included measuring pore pressures after drilling a short interval; and, once the pore pressure was verified, the equivalent circulation density (ECD) and mud overbalance would be optimized. Then drilling would continue to total depth (TD) with periodic FTWD tests along the horizontal section. This drilling strategy required close coordination with on-site drilling operations and petrophysicists and geomechanics and other technical specialists within ADCO.
An important objective of wireline formation testing is the accurate determination of in-situ fluid properties, including density. However, sensors are frequently subjected to multiphase flow when sampling, which can lead to inaccurate determination of the fluid properties and ambiguity in sample contamination analysis. In this paper, we study the behavior of multiphase flow using a density sensor and the implications for the determination of in-situ fluid properties and sample contamination, together with other downhole sensors.A vibrating-tube density sensor operates under the physical premise that its resonance frequency is directly related to the density of fluid within the tube. In reality, however, because of its high sensitivity, the sensor response is influenced by multiple factors, including sensor temperature, pressure, and specific mechanical design configuration. A theoretical study of the physics of a vibrating tube density sensor was performed using a first principle-based approach to optimize sensor characterization and accuracy. By considering all forces acting on the sensor under downhole conditions, a comprehensive theoretical model was established for the vibrating density sensor. This theoretical model is validated using experimental measurements in which we contrast theoretically predicted sensor responses with laboratory-measured responses. We compare these results with log examples using downhole fluid sample results and densities. This paper includes the conclusions derived about the accuracy of measuring fluid densities with this new sensor and a comparison of this measurement with traditional data sources.
The accurate determination of fluid properties and contamination while sampling with a wireline pump-out formation tester is essential to achieve the primary objective of obtaining representative reservoir fluid samples with minimum rig time. Despite advancements in fluid identification sensors, sampling in mixed phases, especially immiscible fluids, still poses a great challenge. It often happens that apparent erratic sensor responses are attributed to sensor noise, but careful study reveals that the sensors are actually showing the true nature of the multi-phase fluid flow. However, if this multi-phase behavior is not considered, it can be difficult to determine fluid type and contamination. This work addresses the development of a new numerical and analytical investigation that makes it possible to not only understand the cleaning behavior of formation fluids but also quantitatively determine fluid qualities in real time. This newly developed technique highlights the variables that play an important role in guiding the clean-up process and, at the same time, provides the temporal characteristics of the contamination level versus both time and fluid volume. Furthermore, uncertainties in the pumping time required to achieve the desired level of contamination are also calculated with this method. Field examples from Gulf of Mexico, South America and North Sea are provided to demonstrate the efficiency of this technique in oil-based mud and water-based mud contamination examples for both hydrocarbon fluid and formation water samples, with comparisons to PVT laboratory measurements. An error analysis is performed for each example, and results are presented in this research.The new analysis technique is applied to a high-resolution fluid density sensor that monitors the change of resonance frequency of a vibrating tube-carrying fluid sample. The same interpretation method is also applied to a capacitance sensor and a resistivity sensor to further confirm the results derived from the density sensor.
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