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Smith, S.. (Baker Hughes) | Elarouci, F.. (Baker Hughes) | Khairy, H.. (Baker Hughes) | Serry, M. A. (ADMA OPCO) | Ahmad, Fazeel (ADMA OPCO) | Al-Feky, M. H. (ADMA OPCO) | Faisal, M.. (ADCO) | Khan, A. H. (ADCO) | Al Reyami, M. M. (ADCO) | Al Kilani, Smeer (ADCO)
Abstract This paper presents the first new technology applications of reservoir fluid characterization and sampling while drilling in the United Arab Emirates. Four case histories provide details of this technology in the last two years, and the value added to the assets operating in different targeted reservoirs. Cost and rig-time optimization demands has motivated operators to utilize the fluid analysis and sampling tool designed for LWD to reach formation targets before they have been exposed to long period of invasion. This technology provides pressure testing, real-time in-situ measurements of formation fluid properties and downhole capture and retrieval of fluid samples. The applications proved valuable in obtaining required formation data and reducing operational time, cost and associated risks. Results of this technology in the UAE were evidenced in the following applications: An offshore field had original formation water with high salinity that, over time, mixed with low salinity injection water which affects water saturation log interpretation. The objective was to collect representative water from the formation (either original formation water or injection water) and this was complicated by water-based mud filtrate with its own unique salinity. Samples from three depths were collected and confirmed by laboratory analysis to be representative formation water. The refractive index provided a clear way of discriminating the water-based mud filtrate from formation water. A field with known condensate was scheduled for fluid sampling to check for injection gas break-through. LWD sampling was used because of the high mobility of the gas and condensate. Seven successful samples were collected and subsequent lab analysis confirmed condensate in the reservoir. Pressure testing and sampling while drilling was performed in a heterogeneous carbonate reservoir. A valid oil gradient was detected after completing several good pressure tests in a short period after drilling. The formation fluid pump-out was initiated to identify and collect oil and water samples that helped in determining an accurate oil-water contact. A fluid sampling operation was performed in a highly deviated offshore well to provide the asset an operational alternative to a complex pipe-conveyed wireline logging operation. The pump-out started shortly after drilling to limit invasion. Five samples were obtained and brought to surface to confirm the real time fluid identification. The case will discuss the challenges and complication of the operation in a highly deviated well crossing several reservoirs. A review of the presented cases helps demonstrate LWD sampling technology as a successful method in the Middle East for characterizing downhole fluid, supporting real-time decision making, minimizing rig time, cost and associated operational risks.
Abstract The traditional way of acquiring reservoir fluid samples (prior to production) has usually involved running a wireline formation tester for several days or even weeks after drilling the well. This time delay between drilling and sampling has an adverse effect on obtaining high quality fluid samples because of long-term exposure to invasion. This effect becomes worse in low permeability formations where effective mud-cake build-up is poor, resulting in deeply invaded formations. In turn, this requires large volumes of filtrate to be pumped back out of the formation in order to collect low contamination reservoir fluid samples. The ability to sample while drilling using LWD technology solves part of this problem by allowing the pump-out to start much earlier in the invasion process, thereby reducing the volume of filtrate required to pump out of the formation. In addition to cost-savings from reduced sampling time, there are other benefits to LWD sampling such as continuous circulation. This can be critical when multiple reservoirs are exposed, some of which may be depleted and pose differential sticking risks, which is often the case in the Middle East. However, current LWD sampling technology is done with a probe which limits the inflow area thereby complicating the sampling process in low permeability formations. Many of the giant carbonate reservoirs in the Middle East are highly heterogeneous and have low average permeabilities (<1-5mD) making it difficult to sample with a standard probe in many situations (LWD technology cannot overcome all the challenges just yet). But viscosity is also critical and the overall mobility of gas reservoirs can be relatively high due to the low gas viscosity, thereby making gas samples a potential application for this new LWD technology in Middle East carbonate reservoirs. Formation pressures and fluid samples were taken from such a reservoir. In this field there is known condensate banking and the project involves re-injecting the produced dry gas into the reservoir to help maximize the condensate recovery. Seven (7) samples were collected using an LWD sampling tool, and subsequent lab analysis on the samples confirmed condensate in the reservoir. This new technology is seen as a way to help maximize recovery and minimize costs.
Over the last two years the experience has shown that logging while drilling (LWD) sampling delivers comparable results to wireline sampling in conventional reservoirs. It is not only beneficial under extreme conditions where a wireline run is technically difficult but also shows its advantages when it is utilized during the drilling operation. It delivers the same fluid quality and reservoir information in less time and with reduced risk.
The paper reviews data collected in the Middle East reservoirs which are often characterized by low mobility carbonates with values below 10 mD/cP. In addition formation fluids can contain large quantities of hydrogen sulfide (H2S). To overcome these challenges special equipment has to be used and special routines are applied. The highly sophisticated pump control system within this LWD fluid analysis and sampling tool improves the clean-up process significantly under these circumstances. The closed-loop control system and different intelligent algorithms avoid pumping below the bubble-point and thus prevent the alteration of the fluid sample. It also delivers additional information about the pumped fluid like the fluid compressibility and precise clean-up mobility. Furthermore it allows for a very accurate adjustment of the pump rate as well as the drawdown pressure. The reading of the integrated fluid identification sensors like optical refractive index, sound speed, density and viscosity will be illustrated to changes of the pump rate, pressure drawdown and existence of multiple phases and fluids. The reservoir response on these parameters will be analyzed and it will be discussed in which cases it can be contra-productive to pump at a high pump speed causing a high differential pressure.
The experience and learning gathered in multiple runs performed in recent years with logging while drilling fluid analysis and sampling tools allows for a broad comparison between different environments as well as different technologies. This includes results from conventional reservoirs, carbonates and shaly sands in different regions around the world. An outlook will be given how this learning improves downhole fluid identification and influences formation evaluation in the upcoming years.
Abstract This paper presents the capabilities and operation of a logging-while-drilling (LWD) fluid analysis and sampling tool in a deep-water application in the Gulf of Mexico. The operation was performed during a drilling run in a high-pressure/high-temperature (HPHT) well with an expected downhole pressure of up to 22,000 psi and 300°F downhole temperature. This paper will show how a robust fluid analysis and sampling campaign was planned and executed, matching the various objectives and technical requirements with the appropriate technology. The challenges and opportunities of LWD sampling will be discussed, especially under tough environmental conditions. The advantages of LWD sampling systems are well known, such as shorter pump-out time due to less invasion and the ability to capture reservoir fluid samples in extended reach drilling or highly deviated wells, which provides a new application range compared to current wireline systems. As the harsh drilling environment generates severe shocks and vibration, it requires precaution in the tool design and the selection of suitable components. The influence of the downhole dynamics on the reliability and durability of the system needs to be considered. In response to these challenges, the new LWD tool incorporates an electro-mechanical driven drawdown pump that further improves the LWD fluid analysis and sampling service. This enables a nearly autonomous operation with the assurance that fluid phase integrity is being maintained. Automation allows optimal use of the available bandwidth to deliver the most complete set of fluid property data in real time for efficient decision making, including density, viscosity, sound speed and refractive index. It enables the operator to monitor the fluid identification (fluid ID) trend carefully and in real time, even from remote locations. The sampling process is performed shortly after the hole is drilled and is therefore subjected to different levels of invasion and contamination arising from the effects of the drilling fluid and the reservoir properties. It will be discussed how this effects the clean-up and the ultimately achievable contamination level. The newly introduced compressibility value derived from the electro-mechanical pump offers a bulk measurement, where localized sensors observe scattered data. Examples from the application in the Gulf of Mexico (GOM) will be shown and discussed. An outlook will be given how this technology evolves in future developments and how the operator and oil company can benefit from the new technologies in the drilling environment.
Hung, Vu Viet (Lam Son Joint Operating Company) | Gia, Phan Phuoc (Lam Son Joint Operating Company) | Van, Nam Nguyen (Lam Son Joint Operating Company) | Hardikar, Nikhil (Baker Hughes) | Pragt, Jos (Baker Hughes) | Kumar, Raveen (Baker Hughes)
The formation evaluation of marginal fields often presents challenges when balancing the value of newly acquired information with the cost of acquiring this information. This case study presents the application of fluid analysis and sampling-while-drilling in two horizontal wells of the marginal Thang Long field in Vietnam. The technology provided critical information about fluid dynamics within the reservoirs enabling timely finalization of completion intervals and avoiding costly future interventions.
The Thang Long field has three main reservoirs in Miocene, lower Oligocene sediments and fractured granitic basement. When formulating the development strategy, horizontal wells (in excess of 1,000 meters horizontal section) were planned with single completion strings. An appraisal plan was also formulated for low-confidence reservoirs. Completion, intervention and workover strategies were thus the dominant challenges for the techno-economics of the project. The first challenge was to finalize the lower Miocene completion targets within the development sub-area with laminated shaly sand (0.5- to 2.0 meters), low resistivities (2.0- to 4.0 ohm-m) outside the vertical resolution of conventional logs; similar to the shale beds and very close to the resistivity of formation water. The total depth of the production wells was designed to be above the oil/water contact to avoid water encroachment, however there were early signs of rise in the water level. The oil/water contact had moved differently than expected during the exploration phase. The second challenge was deciding upon the completion strategy in the exploration sub-area, which included a new appraisal target in lower Oliogocene sands apart from being producers. The environment was influenced by both stratigraphic and structural traps. The compartmentalized sand layers had questionable oil/water contact and estimating representative formation pressure gradients and reservoir fluid sampling was a critical task.
Considering the above scenarios, it was decided to utilize FASTrak sampling-while-drilling technology in two horizontal wells, where deployment of wireline tools on pipe was also not feasible. The fluid characterization and testing jobs during the wiper trips were influenced by high over-balance, up to 1,321 psia (9,108 kPa), and high invasion was expected during the clean-up process. Good stability and repeatability was achieved during pressure testing, leading to high-confidence gradient calculations. The pump-outs were optimized for confident fluid identification and single-phase reservoir fluid sampling. In total, data was acquired with 87 pressure tests. Six pump-outs for reservoir fluid identification were performed from which three were converted to samples.
The application of new generation technology provided early investigation of the reservoirs, based on fluid analysis and sampling-while-drilling. Costly interventions were avoided and overall sample analysis costs were also lowered; each step being critical for favorable techno-economics of marginal fields.