Successful Case of Resin-Based Chemical Sand Consolidation as a Remedial Sand Control Treatment

The Mahakam delta in east Kalimantan, Indonesia, yields gas as the main hydrocarbon production with giant reservoirs ranging from shallow to very deep zones. Reservoirs consists of clean sandstone with high permeability. Due to the field maturity, production gradually moved from the deep, consolidated zones into very shallow, unconsolidated zones. Sand production often causes significant problems at the surface when the well is online. The best approach to sand control is to keep it inside the reservoir, because it could create problems not only at surface but within the wellbore as well. Sand consolidation has been a common approach applied in Mahakam field for more than a decade. Several products have been utilized, including laboratory testing and field trials. The case history is based on a well that had been treated using 2 different sand consolidation products in the past, but both eventually produced inadequate results. Sand continued to break through after each treatment, hence the reserves could not be drained in full. Since the reservoir still had promising reserves, another remedial sand consolidation treatment was planned. This treatment was executed by utilizing a tension packer with a J-slot mechanism in order to focus injection of the resin into the zone of interest. Additionally, there was a challenge with another open zone above the subject interval. The remedial sand consolidation treatment using a resin-based chemical delivered excellent results. Even though this reservoir had been exposed to 2 different chemical treatments in the past, by using the resin-based sand consolidation product, the well was still able to be produced at target rates without sand production. In conclusion, resin-based sand consolidation solutions can unlock prolific reserves that may have been a significant challenge with traditional methods.

Integrated Subsurface Study to Convert Upside Intrabeta Subzone Stakes into Additional Main Targets in Tunu Gas Field, Mahakam Delta, Indonesia

"Intrabeta" is a subzone located in the upper part of Tunu Main Zone between MF3-MF6 regional stratigraphic marker. Total cumulative production from this subzone is at 51 Bcf of gas and 4.96 MMBbl of oil. This interval is situated between Tunu Shallow Zone and Tunu Main Zone, which are the main producing intervals of Tunu Field, a giant mature gas field in Mahakam Delta, Indonesia. With Intrabeta reservoir depositional context more dominated by channel facies and more varied production fluid properties, the development of Intrabeta subzone became more challenging and previously classified as upsides. As Tunu Field is getting more matured, the challenge to deliver infill wells that economically profitable become more arduous. Thus, all attempts to give additional value to the future infill wells should be properly assessed. This paper aims to provide a comprehensive summary of how strategic collaboration between static and dynamic synthesis of Intrabeta subzone has given additional contribution in Tunu Field continuous value creation process. The method started by conducting an extensive post-mortem review on all perforated reservoirs in Intrabeta subzone. Insights from the perforated reservoirs that comprise of production behavior, perforation success ratio, cumulative hydrocarbon production and updated portfolio are then utilized to provide initial prolific area map for future candidates maturation. Data coming from the dynamic analysis were then combined with static depositional analysis on how the hydrocarbon was distributed in Tunu Intrabeta subzone. A new structural map that has been corrected from seismic push-down effect due to shallow gas presence above Intrabeta interval was then utilized to map the structurally promising area. Deterministic channel boundaries and possible sweet spots are then identified and ranked based on the development confidence level. Four wells with additional stakes from Intrabeta subzone have been proposed and drilled in Tunu Main Zone. All wells have successfully found the targeted Intrabeta targets with various post-mortem findings. While in some wells significantly better post-drilling results were encountered, in other cases slightly lower results were found due to static channel development and fluid dynamic uncertainties. All the lesson learned gathered from the pilot wells provide valuable insights on future improvement toward better and more robust Intrabeta candidate maturation methodology. The insights gained from this study have given essential understanding of Tunu Intrabeta subzone characteristics and possible future potentials. Furthermore, this paper provides a comprehensive summary, systematical approach and lesson learned in enhancing previously upside potential of Intrabeta subzone in Tunu Main Zone to compelling additional targets in Tunu Main Zone future wells as part of the continuous value creation process in a giant mature gas field.

One Phase Well OPW : Unlock Shallow Reservoir Efficient and Economically by Eliminating Surface Casing

Tunu is a mature giant gas and condensate field locate in Mahakam Delta, East Kalimantan, Indonesia. The field has been in development for almost 30 years and currently has been considered as a mature field where to put a state of an economic well has become more challenging nowadays. The deeper zone of Tunu has no longer been considered as profitable to be produced and the current focus is more on the widespread shallow gas pocket located in the much shallower zone of Tunu. One phase well is architecture without 9-5/8" surface casing. OPW is one-section drilling using a diverter mode from surface to TD without using BOP. Historical for OPW is began from 2018, where drilling reservoir section using diverter mode in two-phase. In 2018 also succeeded in performing perforated surface casing. Due successfully in drilling operation using diverter and perforated surface casing, in 2019 drilling trials for OPW were carried out. Until now, the OPW architecture has become one of the common architecture used in drilling operations as an optimization effort. Until December 2020 PHM has completed 15+ OPW wells. A general comparison of OPW and SLA well is at the cost of constructing a well of approximately 200,000 - 300,000 US$. The disadvantages of OPW wells are more expensive in the mud and cement section when using a 9-1/2" hole, but in terms of the duration, OPW drilling time is more efficient up to 2-3 days. If viewed from the integrity of the OPW wells, from 15 OPW wells that have been completed, only 2 of them have SCP.

Unlocking Marginal Resources through Synergy between Subsurface and Surface Entities

Tunu is one of the biggest gas fields in Indonesia with 1400 km2 area in Mahakam Delta, East Kalimantan. This field has been producing since 1990 with cumulative production of more than 9.5 tcf and 190 mbbl condensate by the end of 2020 from over 1000 operating wells. Today, Tunu field contributes for approximately 40% of Mahakam production. After 30 years of production, Tunu production level is currently in declining phase, shown by its yearly production profile which exhibits a declining trend since 2008. Furthermore, Tunu well development project was considered marginally economical due to depleting reserve per well. Thus, an integrated study was conducted in order to reduce surface expenditure cost of Tunu pipeline based on current operating parameters. The study consisted of WHSIP history matching to determine new pipeline design pressure, evaluation of future wells production lifetime, and adjustment of pipeline corrosion allowance based on actual corrosion rate observed in Tunu field. Results show that most of future Tunu wells are predicted to have WHSIP below 200 barg and 1.5 to 3 years’ production lifetime. Corrosion rate in Tunu field as measured using corrosion coupon in piping with corrosion inhibitor injection is found to be less than 1 mm/20 years. Therefore, corrosion allowance for Tunu pipeline is optimized from 5 to 3 mm for 10-years design lifetime. For exceptional circumstances where actual well WHSIP > 200 barg, other method of producing the well will be implemented. Hence, by integrating recent subsurface behavior (WHSIP and well lifetime) with surface understanding (corrosion rate), it was then proposed new pipeline design for Tunu development. This study has generated USD 13 million cost saving for pipeline procurement in 2020. Moreover, implementation of the new pipeline design reduces 40% of pipeline unit cost for future pipeline procurement. This study has become the basis for future well development projects in Tunu field which significantly prolong Mahakam's production sustainability.

Waterbirds roosting on gas drilling platforms in Mahakam Delta, East Kalimantan: the Unexpected Impact of Landscape Transformation

Since 2014 some offshore gas platforms operated by Pertamina Hulu Mahakam near Mahakam Delta has been used by hundreds of egrets as roosting sites, causing nuisance to the platform and hampering the duty of workers/operator. The objective of this paper was to analyse the situation of the waterbirds’ nuisance, analyse the possible causes, and provide some recommendations. Field visits were conducted in August 2019 and February 2020 to three unmanned platforms (Ax, D, C) that suffered the most from the bird roost. Birds that infested the platforms were identified as great egret and intermediate egret, both are very similar in appearance and ecological requirements. The maximum number of egrets visiting C-Platform (the worst platforms) was 671 birds. These birds roost at night in the platform and leave the platform in the morning to forage for fish, eel, and shrimps in the wetlands of Mahakam Delta, about 2-4 km from the platform. The root cause of the infestation was believed to be the landscape transformation in the Mahakam Delta. Mangrove forest has been diminished and heavily converted into shrimp-ponds. The egrets’ foraging areas became ubiquitous, while the roosting/nesting site greatly decreased, forcing the egrets to roost on gas platforms. In the short-medium term, platforms need to be managed as bird tolerated-zone and bird-free zone (using deterrent), while in the long term, land-use in Delta Mahakam need to be restored.

First Application Drilling New Wells with HWU in Swamp Environment, Mahakam Delta

Tunu is a mature giant gas and condensate field locate in Swamp Area on Mahakam Delta, East Kalimantan, Indonesia. The field has been in developed for more than 40 years and considered as a mature field. As mature field, finding an economic well has become more challenging nowadays. The deeper zone of Tunu (TMZ) has no longer been considered profitable to be produced and the focus is shifted more on the producing widespread shallow gas pocket located in the much shallower zone of Tunu (TSZ). Facing the challenge of marginal reserves in the mature field, Pertamina Hulu Mahakam (PHM) take two approaches of reducing well cost thus increase well economics, improving drilling efficiency and alternative drilling means. Continues improvement on drilling efficiency by batch drilling, maxi drill, maximizing offline activities and industrialization of one phase well architecture has significantly squeezed the well duration. The last achievement is completing shallow well in 2.125 days from average of 6.5 days in period of 2017-2019. Utilization of Swamp Barge Drilling Rig on swamp area had been started from the beginning of the field development in 1980. Having both lighter and smaller drilling unit as alternative drilling means will give opportunity of reducing daily drilling rate. Hydraulic Workover Unit (HWU) comes as the best alternative drilling means for swamp area. In addition, fewer and smaller footprint equipment requires smaller barges with purpose of less civil works to dredge the river and preparing well location. Drilling with HWU project has been implemented at Tunu area with 5 wells has been completed successfully and safely. HWU drilling concept considered as proven alternative drilling means for the future of shallow wells development.

Mature field Development to Periphery Area: Tambora West Flank development

Tambora gas field, discovered in 1974 is located in a swamp area at the apex of Mahakam Delta, and it is adjacent to Nilam field, which is operated by another operator. Geologically, the Tambora and Nilam Fields have the same anticline structure that originates from the sediment provenance west of Kalimantan as reflected in present day Mahakam Delta. Therefore, this study aims to analyze the challenges to unlock the potential of the west flank area of Tambora Fields. The geological synthesis of both Tambora and Nilam fields shows similar net sand and pay distribution in lateral and vertical proportions. Most developments in the Tambora Anticline area are in the crest and the distances between wells are ~100-200m. Challenges to unlock potential in flank areas are derived from the limitation of wells and seismic data. Based on data and knowledge of the flank areas in both fields, the west flank has better productivity compared to the east. Therefore, geological synthesis is conducted in the west flank area to define hydrocarbon and reservoir properties. Furthermore, channel models were made from 2D seismic scouring, controlled by the continuation of well log channel facies in the anticline crest area. Based on the preliminary approach, 3 wells were proposed to unlock west flank Tambora potential and were integrated into the plan of development. Primarily, dynamic uncertainty affects the potential of the west flank since production in the anticline crest area is enormous, and the uncertainty was analyzed by drilling one recent well. The result shows that hydrocarbon in the flank is not fully connected with the anticline crest area and has proven the sidebar heterogeneity concept. These gave more confidence to seek further positive results and develop west flank Tambora to sustain Mahakam production in the future.

Machine Learning Technology to Improve Precision and Accelerate Screening Shallow Gas Potentials in Tunu Shallow Gas Zone, PT Pertamina Hulu Mahakam

Tunu is a giant gas field located in the present-day Mahakam Delta, East Kalimantan, Indonesia. Tunu gas produced from Tunu Main Zone (TMZ), between 2500-4500 m TVDSS and Tunu Shallow Zone (TSZ) located on depth 600 - 1500 m TVDSS. Gas reservoirs are scattered along the Tunu Field and corresponds with fluio-deltaic series. Main lithologies are shale, sand, and coal layers. Shallow gas trapping system is a combination of stratigraphic features, and geological structures. The TSZ development relies heavily on the use seismic to assess and identify gas sand reservoirs as drilling targets. The main challenge for conventional use of seismic is differentiating the gas sands from the coal layers. Gas sands are identified by an established seismic workflow that comprises of four different analysis on pre-stack and angle stacks, CDP gathers, amplitude versus angle(AVA), and inversion/litho-seismic cube. This workflow has a high success rate in identifying gas, but requires a lot of time to assess the prospect. The challenge is to assess more than 20,000 shallow objects in TSZ, it is important to have a faster and more efficient workflow to speed up the development phase. The aim of this study is to evaluate the robustness of machine learning to quantify seismic objects/geobodies to be gas reservoirs. We tested various machine learning methods to fit learn geological Tunu characteristic to the seismic data. The training result shows that a gas sand geobody can be predicted using combination of AVA gather, sub-stacks and seismic attributes with model precision of 80%. Two blind wells tests showed precision more than 95% while other final set tests are under evaluated. Detectability here is the ability of machine learning to predicted the actual gas reservoir as compared to the number of gas reservoirs found in that particular wells test. Outcome from this study is expected to accelerate gas assessment workflow in the near future using the machine learning probability cube, with more optimized and quantitative workflow by showing its predictive value in each anomaly.

One Phase Well (OPW): Unlock Shallow Reservoir Efficiently and Economically ay Eliminating Surface Casing

Tunu is a mature giant gas and condensate field locates in Mahakam Delta, East Kalimantan, Indonesia. The area has been developed for almost 30 years and is currently considered a mature field, where putting a state of an economical oil well has become more challenging nowadays. The deeper zone of Tunu has no longer been considered profitable to be produced. The current focus is more on the widespread shallow gas pocket located in the much more external area of Tunu. One phase well is architecture without 9-5/8" surface casing. OPW is one-section drilling using a diverter mode from surface to TD without using BOP. Historical for OPW is began from 2018, where drilling reservoir section using diverter mode in two-phase. In 2018 also succeeded in performing perforated surface casing. Due to a successful drilling operation using diverter and perforated surface casing in 2019, drilling trials for OPW were carried out. The OPW architecture has become one of the standard architectures used in drilling operations as an optimization effort. Until December 2020, PHM* has completed 15+ OPW wells. A general comparison of OPW and SLA well is at the cost of constructing a well of approximately 200,000 - 300,000 US$. The disadvantages of OPW wells are more expensive in the mud and cement section when using a 9-1/2" hole. But, OPW drilling time is more efficient in terms of the duration, up to 2-3 days. Based on the integrity of the OPW wells, from 15 OPW wells that have been completed, only 2 have SCP.