Production Optimization Coupling Multiple Reservoirs and Facilities With Sour Gas Re-Injection for Miscible EOR in South Oman

Effective gas utilization is critical to any gas injection development project to maximize recoveries for a given purchase of make-up gas, whilst reducing the Green Gas House (GHG) emissions. This paper describes the use of a fully implicit Integrated Production System Model (IPSM) for two inter-connected production system networks, coupling multiple, critically sour oil reservoirs undergoing Miscible Gas Injection (MGI) for Enhanced Oil Recovery (EOR) using produced sour gas from oil and condensate fields in South Oman. The IPSM model links sixteen reservoir models with varying levels of complexities to the facilities network. Complexities in the facilities include multiple nodal constraints that necessitate the use of an Equation of State model (EOS). The IPSM model honors the gas balance implicitly. Gas flood optimization includes prioritizing low GOR production wells (at reservoir and well level) whilst maintaining reservoir pressure above Minimum Miscibility Pressures (MMP). Development schedule optimization also helps in optimizing the compressor size, the key Capex component. Compositional modeling allows continuous tracking of souring levels at different nodes, providing integrity status of overall production system network. The current IPSM model helps in optimization of schedule for the phased development of the oil reservoirs and eventually the most efficient gas utilization. This has enabled low pressure operation in some reservoirs providing oil at very low unit technical cost while waiting for gas availability. Compositional tracking for H2S helps in operating the facilities within design limits whilst planning future developments to cater to this design. Some key parameters can be parameterized for quick sensitivity analysis for an informed decision making for business opportunities. The production potential of the system is also tracked to ensure there is a cushion in the system to deal with any unexpected changes. This feature helps in planning and optimizing the scheduled turn-around activities for these two inter-connected production system networks. The novelty of this work is collaboration across multiple disciplines, especially the surface and subsurface because of complex interactions between facilities constraints and reservoir performance (associated with produced gas reinjection). Compositional tracking and injection gas apportionment across multiple reservoirs is key to the overall value maximization in this complex development.

Best Practices While Testing Sour GAS Wells

Objectives/Scope The development of Abu Dhabi's sour gas is not without its challenges. Deep drilling in some fields presents its own set of difficulties due to high temp and pressures coupled with +30% H2S and +10% CO2. Handling of these corrosive reservoir fluids both while drilling and then testing, requires deploying advanced technology to meet the specific requirements of these reservoirs, along with the infrastructure necessary to handle the toxic and corrosive products while testing in a brown field safely. Methods, Procedures, Process Developing local sour gas production is seen as the answer to resolve the ever growing energy needs for UAE but the technical requirements for the project is stretching the limits of the industry. Results, Observations, Conclusions What did we do different: Developed and implemented specific HSE procedures and SIMOPS due to close proximity with major populated facilities which could not be shut-down during the testing period. Conducted multiple audits and drills with the local authorities including Civil Defense and local Police. Additional 3rd part supervision was provided to ensure all personal are complying with the policy and procedures developed. Installed 2 green burners and 2 vertical 90 ft flare stacks at 180 degrees. This was to cater for the changing wind directions for continuous operations and as back ups. CCTV monitoring for green burners / flare stacks was conducted although this was a rigless operation 3 circles of H2S detectors and sensors were placed around the testing area and the flare stakes and green burners to detect any H2S gas. (Covering all 360° directions). Blowdown/Depressurization valve was installed at separator, storage tanks apart from Automatic and manual shutdown system upon H2S detection Installed Optic Fiber cable from wellhead to the main control room for monitoring purposes All piping connections used were flange-to-flange as welded joints could have caused stress cracking on the weak points For Sour well operation, used fully cladded X-mass tree & Inconel well completion Considered setting of compatible TTBP (Thru Tubing Bridge Plug) for staked reservoirs zonal isolation Instead of coil tubing cement plug for accurate depth calculations. Arranged Special chemical for any scale cleanout for handling of elemental Sulphur. Arab zones were stimulated with specialized acid recipe developed exclusively for this temperature, pressure and sour conditions downhole. Bottom hole measurements were recorded successfully and all the necessary data was acquired. Novel/Additive Information This paper highlights the major challenges identified and mitigated to test and produce the highly sour HPHT gas during the appraisal program complying with ADNOC 100% HSE in a brown field without disturbing the other major operations being performed in the vicinity.

Gas Wells with Carbon Steel Completion, Can it Handle Sour Gas Production, Case Study

Title Gas wells with Carbon steel completion, Can it handle sour Gas production, Case Study. Objective/Scope It is a successful case of producing sour gas (up to 18% H2S and 9.2% CO2) since 2016 wells with carbon steel tubing with maintaining downhole chemical injection of corrosion inhibitor. Methods, Procedures, Process During 2014 a group of new wells has been drilled in X giant onshore gas reservoir under ADNOC onshore company operating area to maximize gas production and to meet production mandate. Majority of wells has been drilled within the North and peripheral Area of the reservoir. All wells has been completed with a standard completion with a Top completion (+/-7000 ft.) in carbon steel with downhole chemical injection valve, and a corrosion resistant alloy section below the CIV. After wells commissioning, high H2S contents were observed (Up to 18%), and Management initially instructed operations to shut in 9 wells and formulated a task force to study the applicable options and analyze the data to ensure asset integrity. The TF recommendation was to flow the wells with close monitoring of wells integrity, in particular annulus pressure A comprehensive downhole exercise has been done by Results/Observation/Conclusion Carbon steel completion with downhole chemical injection is a validated completion solution for such conditions. Novel/ Additive information Clearly, case is as a solid reference for sour gas production using conventional completion, sustaining Long-term production is adding more weight to the case conclusion.

PENGARUH LAJU ALIR ABSORBEN DAN WAKTU KONTAK K2CO3 TERHADAP PENYERAPAN CO2 YANG TERKANDUNG DALAM GAS ALAM

Gas CO2 atau gas asam (sour gas) merupakan salah satu kandungan dari gas alam yang sifatnya sebagai kontaminan. Adanya kandungan gas CO2 yang tinggi didalam gas alam perlu dilakukan treatment khusus dalam menghilangan kandungan gas asam (sour gas) tersebut dari gas alam dimana proses penghilangan gas asam dari gas alam disebut proses Sweetening. Proses Absorspi gas CO2 merupakan metode yang sering dilakukan. Penelitian ini bertujuan mengetahui pengaruh laju alir absorben dan waktu kontak terhadap konsentrasi CO2 yang di serap. Metode yang dilakukan dalam penelitian ini yaitu dengan perancangan alat yang bisa menunujukan proses absorpsi CO2. Variabel penelitian yang digunakan memvariasikan laju alir absorben 4,95 ml/s, 7,26 ml/s, 10,75 ml/s serta waktu kontak 2,4,6,8 menit dengan menggunakan absorben K2CO3 dan Gas alam yang digunakan compress Natural Gas CNG. Dari hasil penelitan laju alir Absorbenyang paling baik didapat pada 10,75 ml/s dengan penyerapan CO2 sebesar 69,45 %. Waktu kontak pada setiap waktu tidak berpengaruh banyak terhadap konsentarsi CO2 yang terserap . Kata kunci: absorben, Sour gas, gas alam, laju alir AbstractCO2 gas or acid gas (sour gas) is one of the contents of natural gas which is a contaminant. The presence of high CO2 gas content in natural gas requires special treatment to remove the sour gas content from natural gas where the process of removing acid gas from natural gas is called the Sweetening process. The CO2 gas absorption process is a method that is often used. This study aims to determine the effect of absorbent flow rate and contact time on the absorbed CO2 concentration. The method used in this research is to design a tool that can show the CO2 absorption process. The research variables used varied the absorbent flow rate of 4.95 ml/s, 7.26 ml/s, 10.75 ml/s and a contact time of 2,4,6,8 minutes using K2CO3 absorbent and natural gas used compressed Natural CNG gas. From the research results, the best absorbent flow rate was obtained at 10.75 ml/s with CO2 absorption of 69.45%. Contact time at any time did not have much effect on the concentration of CO2 absorbed. Keywords: absorbent, sour gas, natural gas, flow rate

Injection and Production Optimization for Tengiz Platform Sour Gas Injection by Reactive and Proactive Conformance Completions Control

Sour gas injection operation has been implemented in Tengiz since 2008 and will be expanded as part of a future growth project. Due to limited gas handling capacity, producing wells at high GOR has been a challenge, resulting in potential well shutdowns. The objective of this study was to establish an efficient optimization workflow to improve vertical/areal sweep, thereby maximizing recovery under operation constraints. This will be enabled through conformance control completions that have been installed in many production/injection wells. A Dual-Porosity and Dual-Permeability (DPDK) compositional simulation model with advanced Field Management (FM) logic was used to perform the study. Vertical conformance control was implemented in the model enabling completion control of 4 compartments per well. A model-based optimization workflow was defined to maximize recovery. Objective functions considered were incremental recovery 1) after 5 years, and 2) at the end of concession. Control parameters considered for optimization are 1) injection allocation rate, 2) production allocation rate, 3) vertical completion compartments for injectors and producers. A combination of different optimization techniques e.g., Genetic Algorithm and Machine-Learning sampling method were utilized in an iterative manner. It was quickly realized that due to the number of mixed categorical and continuous control parameters and non-linearity in simulation response, the optimization problem became almost infeasible. In addition, the problem also became more complex with multiple time-varying operational constraints. Parameterization of the control variables, such as schedule and/or FM rules optimization were revisited. One observation from this study was that a hybrid approach of considering schedule-based optimization was the best way to maximize short term objectives while rule-based FM optimization was the best alternative for long term objective function improvement. This hybrid approach helped to improve practicality of applying optimization results into field operational guidelines. Several optimization techniques were tested for the study using both conceptual and full-field Tengiz models, realizing the utility of some techniques that could help in many field control parameters. However, all these optimization techniques required more than 2000 simulation runs to achieve optimal results, which was not practical for the study due to constraints in computational timing. It was observed that limiting control parameters to around 50 helped to achieve optimal results for the objective functions by conducting 500 simulation runs. These limited number of parameters were selected from flow diagnostics and heavy-hitter analyses from the pool of original 800+ control parameters. The novelty of this study includes three folds: 1) The model-based optimization outcome obtained in this study has been implemented in the field operations with observation of increased recovery 2) the hybrid optimization of both schedule and operation rule provided practicality in terms of optimization performance as well as application to the field operation 3) provides lessons learned from the application of optimization techniques ranging from conventional Genetic Algorithm to Machine-Learning supported technique.

Prediction of Dynamical Changes Hydrogen Sulfide Concentration During South-West Gissar Gas-Condensate Fields Development

An unexpected raise of hydrogen sulfide levels during development of several gas condensate fields in Southwestern Gissar, producing from naturally fractured carbonate reservoirs, observed within a year, lead to necessity of full scale comprehensive investigation. For planning of effective mitigation strategy important questions related to the reasons of hydrogen sulfide level growth and prediction of its further behavior have been addressed in the present study. The entire investigation process encompassed both theoretical and practical parts. Theoretical part covered evaluation of sour gas sources that was crucial in respect to selection of conceptual methodology for predictions. All possible contributing sources including primary and secondary have been investigated to discern the causes and consequences of hydrogen sulfide occurrence. Practical component of the study employed cut to edge technologies tested and implemented in reservoir simulation. Based on conceptual constraints with the use of existing field data, interpretation results and regional knowledge basin and 3D static models with fracture network have been developed. Obtained modeling results have been integrated into compositional model, allowing to predict with applied uncertainty analyses further H2S content change during field development.

Experimental Study on the Elemental Sulfur Solubility in Sour Gas Mixtures

The investigation of elemental sulfur solubility plays critical roles on sour gas reservoir development. In this paper, the solubility of elemental sulfur was directly measured by static method with gas samples from well M1 of a sour gas reservoir in Sichuan Basin. The results show that the solubility of elemental sulfur ranges from 0.001 g/cm3 to 0.968 g/cm3 at 40–98.9 MPa and 15–49.8 MPa. The elemental sulfur solubility increases with increasing temperature and pressure, especially when the pressure is greater than 30 MPa. Moreover, the H2S content in sour gas mixtures is also an important factor affecting elemental sulfur solubility. The elemental sulfur solubility increases with increasing H2S content of the sour gas mixtures. The experimental data in this paper display a consistent trend with the reported experimental data. Based on the experimental results, the chrastil-type model, Robert’s model and Hu’s model were investigated and compared. The results show that the chrastil-type model by fitting experimental data in this paper has less error and higher accuracy in calculating elemental sulfur solubility in M gas reservoir. The chrastil-type models proposed in the literature, meanwhile, are only based on the regression of specific gas components and experimental conditions, which lead to a large error in the calculation of elemental sulfur solubility of sour gas samples in this research. The research results provide important basic data and technical support for the development of M gas reservoir.