Mahakam block with one of its gas fields, Tunu, has been developed for decades. Hundreds of wells were drilled to unlock layered sand reservoirs ranging from unconsolidated to consolidated reservoirs. Through field experience, well architecture is actively developing. The latest architecture, targeting shallow reservoirs only, is called Shallow Light Architecture (SLA). The well is completed with 3.5in production tubing cemented inside a 8.5in open-hole reservoir section. SLA is the default architecture for chemical sand consolidation (SCON) or thru-tubing screens as subsurface sand control. Perforation is performed by deep penetration (DP) hollow-carrier guns deployed with double-density to maximize open area and reduce sand production risk. DP charges were used based on the requirement to bypass near-wellbore damage, which is the same practice used in consolidated sand reservoir perforating. As more marginal reservoirs need to be unlocked, big entrance hole (BEH) perforation was initiated for the current sand control optimization alternative by SCON chemical reduction with shorter perforation intervals; and for thru-tubing metal screen performance improvement by placement in front of perforation entrance tunnels with minimum erosion risk. BEH was then studied as it has never been used previously in Mahakam with thru-tubing applications. Simulation and pilot well trials were explored to ensure that a short penetration would not significantly impact reservoir delivery on SLA wells. Inflow performance relationship (IPR) analysis resulted in slight additional drawdown compared to the calculated drawdown using DP at 2.5 MMscfd as an average gas rate in current thru-tubing sand control, which was considered acceptable from the operating envelope perspective. In total, BEH perforation was executed on ten wells with reservoir permeability range from 220 millidarcy (mD) to an extreme case of 3000 mD. Various SCON treatments were injected at optimized perforation lengths by cutting chemical costs up to 60% with sand-free production at a particular parameter and chemical type. On the other hand, in the application using screens, evaluation was not conclusive due to screen sizing issues for some installations. However, in-situ gas velocity could be reduced to the theoretical erosion velocity limit for a metal screen. This new approach to BEH charges utilization has a potential solution optimizing current SCON costs while also reducing erosion risk for the through tubing screen application to improve its performance. By using short penetration of charges, this approach was successfully implemented without jeopardizing reservoir's deliverability.
Mahakam block has supported Indonesia's Oil and Gas production with over 40 years of deliverability. Presently, along with its maturity cycle, comes the challenge of a steeply declining matured field with indicators of marginal reserves, included unconsolidated sand reservoirs as one of the main contributors which required sand control. In addition, future offshore platform development emerged the urgency of light deployment and robust sand control. Deep dive into the methodology, it was mandatorily to revisit what techniques available on the shelves and what is the current technology has to offer. Mahakam subsurface sand controls were classified into gravel pack, open hole stand-alone screen, chemical sand consolidation (SCON), and thru-tubing metal screen. These also respectively account for the highest to the lowest of operational investment, associated production contribution, and its reliability. Thru tubing screen methodology in cased-hole application showed weakness by plugging and erosion issue resulting on minimum utilization as lowest end subsurface sand control means. Several normative elements factored into it, with the root cause of screen placement. It was avoided to install metallic screen in front perforation due to direct jetting during the natural sand packing (NSP) process, causing an installation at slightly above perforation with the absence of stable NSP and screen size selection complexity. Thru-tubing screen with higher strata of material, silicon carbide or ceramic, was selected as a pioneer on new installation philosophy to tackle erosion issue. It was combined with the developed Mahakam sand grain size map as a screen size selection guideline. A confidence pseudo-straddle thru-tubing ceramic screen (TTCS) installation campaign in front of perforation interval was explored on swamp (Tunu) and offshore (Peciko) gas wells. This technique adopts open hole SAS with retrievable concept optimizing slickline intervention. Perfection of the techniques is a process that continues. However, based on the current study and trial results on wells installation throughout 2020 to 2021, positive results were achieved: Operation simplicity with minimum operation HSE risk, Sand free production delivery addressing highly unconsolidated reservoir with widely distributed sand grain by mitigating the risk of screen erosion, The average cost savings were 66% in delta and 76% in offshore compared to allocated SCON budget, Cummulative gas deliverability increased by more than 200% compared to previous thru-tubing metal screen performance, Performance exceeded average SCON production rate and in-situ gas velocity limit at several installations, The installation method had a 100% retrievability success ratio from all retrieval attempts on inactive wells installation, It had no damaging effect to the reservoir when remedial by SCON was required, The installation concept adoption has been proven on highly deviated and unique completion configurations. This enlightenment boosted confidence in both the assessment technique and installation philosophy. This initiative would enable the production of Mahakam marginal sandy reservoir while sparking to a wider application as an alternative robust and light sand control solution.
Since first time introduced in oil & gas well by Gilbert (1954) then popularized by Mach (1979) and Brown (1984) as Nodal Analysis™, system analysis is commonly used to analyze the performance of system composed of multiple interacting components. It is generally used for well diagnostic, performance matching, and prediction for optimization. In this concept, multiphase flow modeling in steady-state condition also introduced and widely used in industry to analyze flow performance inside wellbore with empirical or mechanistic approach. However by its nature, flow performance always as transient flow phenomenon and several cases could not be captured by steady-state model. Dynamic well modeling is needed to verify some of the conclusions from steady-state simulation therefore uncertainty could be reduced. Dynamic model features mechanistic & empirical approach with basic conservation equations (mass, energy, momentum), constitutive correlations and flow pattern transition modeling (Benidiksen et al, 1991; Staff et al., 2015). It is a powerful approach to generate model where dynamic-transient phenomena is become concern. Dynamic well modeling has been demonstrated in latest 5 years of Mahakam operation for specific purpose where steady-state well model which regularly used could not represent dynamic condition. Several studies are presented in this paper with certain objectives for well diagnostic, optimization, risk analysis or in general for petroleum engineering purpose: 1) Liquid loading prediction; 2) Well start-up prediction & analysis; 3) Static condition requirement analysis for well revival campaign; 3) Velocity String performance prediction; 4) Alternative water production estimation where direct measurement has limitations; 5) Wellhead shut-in pressure prediction with buffer zone effect to support unlocking high pressure reservoirs; 6) Blow-out modeling and dynamic well killing for blow-out contingency plan; 7) Unstable gas lift injection phenomena that impact to liquid production; 8) Liquid accumulation inside pipeline which impact to well back pressure, etc. The advantage and drawbacks from model implementation also presented as a practical reference to consider this approach. In summary, dynamic well modeling is beneficial in Mahakam operation, moreover in today's mature condition (operated more than 40 years) where the problem becomes more complex and better decision making is needed to consider efficient method with effective cost.
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