The Nong Yao field is a marginal oil field that presents many challenges, both geological (thin hydrocarbon column and structural uncertainty due to shallow gas effects) and with well design (shallow depth and unconsolidated reservoirs). The field has been on production for almost five years with water cut in most wells now over 90%. The key to extending field life is identifying new infill locations, with advanced technology required to identify and drill these targets. To improve seismic image and structural definition, the seismic data was reprocessed in 2016, utilizing the latest technologies including Broadband Processing and Full Waveform Inversion. This detected local unswept structures and thin reservoirs allowing for identification of infill targets. New generation hydrocarbon saturation cased hole logs were run in wells to identify swept versus bypassed oil areas. Many infill opportunities required complex 3-D well trajectories and innovative completions. To achieve these objectives, technology such as high build rate rotary steerable systems, advanced real time survey corrections, a multilayer bed boundary detection tool, rotational friction transducer and inflow control devices were implemented. After four years of production, a key well exhibited significantly more production than expected, indicating a much larger reservoir than modelled. However, water cut in this well had reached 98%, so infill wells were required in order to extend production. The reprocessed seismic indicated that the structure extended further to the east of the existing producer than initially modelled. A cased hole saturation log was acquired in an existing well drilled near the planned landing location, which showed that the reservoir was actually swept in this area. Instead, the infill well was landed and drilled in the opposite direction in this eastern part of the structure, keeping the heel away from the water, but providing a much more challenging well path. A high-build rate rotary steerable system, advanced real time survey correction and rotational friction transducer were used to safely deliver this complex 3-D well profile and avoid collision risk from offset wells. The multilayer bed boundary detection tool was then used to ensure the horizontal well stayed as high as possible whilst remaining within the reservoir. Lastly, an inflow control device was installed in the horizontal section to delay water production. The well came online with 0% water cut and is an excellent producer. Similar methods have been adopted at other locations to identify and drill infill targets with great success. Collaboration across disciplines is key, as input is required from the geologist, geophysicist, petrophysicist, reservoir engineer, drilling engineer and completion engineer to identify, drill and produce these infill targets. Implementation of this approach continues to add new volumes and extend field life.

This paper describes the successful application of Autonomous Inflow Control Device (AICD) technology in the Nong Yao oil field located in Block G11/48 within the Gulf of Thailand. Water injection in the Nong Yao field, is often into unconsolidated sands drained at different depletion levels. This can lead to formation failure and the transportation of sand back through the annulus and tubing. This AICD bypass valve technology provides a solution by only allowing injected water into the formation but not in the opposite direction hence preventing downhole crossflow. An AICD Bypass Valve was installed into two injection wells that were completed as Multi Zone Completions (MZC). It was planned that multiple zones would be opened simultaneously to provide ongoing waterflood support. The expectation was that the AICD technology would prevent crossflow between zones, due to pressure difference during any injection shutdowns, thereby eliminating the chance of formation failure and transportation of sand from the reservoir into the annulus and tubing. At first, these reservoirs were produced through depletion, and waterflood of these reservoirs did not commence until reservoir pressures had reached between 5.5–7.0 ppg. This led to differential depletion across these reservoirs, hence increasing the risk of downhole crossflow immediately upon any injection shut down, which may come with sand production resulting injectivity impairment. This has been observed across other wells in the field not fitted with AICD Bypass Valves. The concept of the AICD Bypass Valve is that the device requires a positive injection pressure differential to activate and open and allow fluid to pass through and it will close if the well is shut in due to a drop in the required pressure for valve activation. Since the installation of AICD Bypass Valves, these wells have been shut in multiple times due to platform shutdowns for rig mobilization and each time no drop in injectivity has been observed on restart, and sand production has been observed as predicted. AICD Bypass Valves were installed into two new injection wells in the Nong Yao field, providing a low cost alternative to recompletion or redrill that may be required, if screens become plugged due to sand production triggered by crossflow between reservoirs during well shut-in. This has provided more reliable production for the field and the success in this project means that more AICD Bypass Valves will be planned for future MZC, for injection wells in unconsolidated sand.

The recent development drilling campaign at Mubadala Petroleum's offshore Nong Yao field faced many challenges, one of which is the complexity of the reservoir which consists of mixed sand-shale sequencies with thin sand lobes of varying thicknesses. To tackle these challenges and to maximize recovery, Mubadala Petroleum planned four horizontal wells for this campaign. However, the conventional methods of geosteering have limitations. For instance, the distance-to-boundary mapping tool typically does not provide large enough depth-of-investigation for the operator to see through the interbedded shale layer to identify the multiple target sand lobes, which could pose limits on the production optimization and ultimately on the final recovery rate. Fortunately, a new technology emerged at the start of the campaign with a potential for a much larger depth of investigation and a better mapping resolution. This multilayer mapping-while-drilling tool was an extension of the previous tool with additional sensors that could read deeper into the formation. Coupled with a new advanced automatic inversion process which utilizes powerful Cloud computing, the subsurface formation resistivity profiles around the wellbore could be mapped clearly up to 25 ft away from the tool, while providing a multilayer mapping with up to 8-layer mapping capability. This new technology was evaluated and applied in two wells in this campaign to resolve the above-mentioned challenges. The result was a resounding success for the Mubadala led drilling team. In this paper, the authors explain the technology, the process of evaluating and applying it to operation, and the results from applying it. This was the first time that this technology was used in Thailand and this case study summarizes a successful outcome. The mapping results from the tool will also be used to update the reservoir model during the post-job phase and provide improvements of the overall reservoir characterization of the field.

This paper presents the successful application of a new-generation slim pulsed neutron logging tool for identification of bypassed oil in the Nong Yao field. The field comprises of different small pools of oil developed with horizontal wells. The wells are drilled with long lateral sections to increase the drainage area in an attempt to increase sweep efficiencies. However, the sweep efficiencies remained uncertain given reservoir heterogeneity and the nature of water encroachment into the wells. Reservoir saturation monitoring through tubing is usually required for an effective reservoir management program in such a mature field, and a cost-effective method for future opportunity identification. The traditional slim pulsed neutron logging (PNL) tools often provided inconclusive results especially when deployed in complex completion conditions. A new-generation slim pulsed neutron logging tool, which provides high-resolution spectroscopy with a much-improved accuracy and precision was investigated and introduced. This tool delivers self-compensated sigma and neutron porosity measurements in a wide range of conditions, including complex completions and with varying amount of gas in the wellbore or annulus. This new PNL tool was run in the Nong Yao field in December 2017 with the objective to prove the remaining oil at the top of a reservoir. The objective was to acquire data in GSH (sigma, fast neutron cross section, Porosity) and IC (spectroscopy) modes in 8-1/2" hole with conventional completion (7" casing + 2-7/8" tubing). Despite challenging borehole fluid conditions, the data acquired confirmed remaining oil in the reservoir and a new well drilled in 2018 targeting this bypassed oil is currently producing with very good oil production. This successful implementation of PNL in 2017 led to the adoption of the tool as a good alternative for confirming bypassed oil in the Nong Yao field. This strategy has been adopted for well target validation and horizontal well placement to support the 2019-2020 infill drilling campaigns. In December 2018, this tool was run again in three selected candidate wells to prove the remaining bypassed oil and oil saturation away from currently producing wells. The results acquired in all three cases showed clear oil/water contact movement and sweep where present, confirming sufficient remaining oil volume to justify the drilling of new infill wells to develop these volumes during the 2019-2020 infill drilling campaigns. The new generation PNL tool provides a low-cost alternative for effective reservoir depletion monitoring. Proper reservoir management, additional opportunity identification, and infill drilling target optimization are all benefits that can accrue from accurately locating bypassed oil. Field development plans can then be further optimized, resulting in increased asset value.

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