Proper and reliable resource assessment of hydrocarbons in-place and recoverable volumes is one of the key factors in field development planning (FDP) and determines the commitments made to the host government for the reserves to be developed (RTBD). Many times, it is critical to update the resources and reserves of a producing asset through full field reviews (FFR) to gauge the production attainment and success of initial forecasts in FDP and also to locate any upside/locked-in potential.
Often uncertainties in the field development are expected to reduce as the field produces, but in many cases the results show otherwise due to lack/ inaccuracy of data or existing reservoir complexities. This paper elaborates how an integrated approach utilizing analytical methods (material balance, pressure and rate transient analysis) combined to numerical reservoir simulation is used for accurate resource assessment of an over-pressured gas condensate reservoir that suffers from lack of geological and petrophysical data, faulty production data measurement system and complex fluid and pressure behavior.
A comprehensive workflow comprising of different methodologies is used to harness the available geological, petrophysical, production and pressure data. Over-pressured and compressibility corrected gas material balance and pressure and rate transient analysis (RTA) are conducted using static and flowing data to encompass the existing uncertainties on resource numbers and generate low, base and high cases. The results of these methods are then successfully utilized to construct the dynamic reservoir model for evaluation of the upside and near field exploitation (NFE) potential. The results of the full field review lead to a 50% increase in the gas initially in-place compared to FDP volumes and a significant addition in the proven reserve. This increase in volumes was investigated through proactive surveillance for a period of time and was well supported by the reservoir and well performance.
A novel approach to numerically model the over-pressured gas reservoirs is developed using a simple concept of compressibility modifications supported by production data history match and analogue core data. The results of the study greatly benefited the production sharing contract (PSC) and lead to production enhancement from the field through a proper debottlenecking project.
Rate Transient Analysis (RTA) has been used in gas reservoirs as a proven method for reserve estimation, well diagnostic and production performance evaluations. The authors have demonstrated several case studies showing the application of production analysis (PA) for reservoir characterization in gas and single phase oil reservoirs previously (
These methods were found to be extremely powerful and popular particularly with the high resolution data from pressure downhole gauges (PDG).
In this paper we have analyzed the available production data from a gas reservoir in offshore environment in South East Asia. It has been developed with five high PI wells and smart completion and monitored closely with PDG and other surveillance data to understand the contact movement during the production history. Due to the complexity of the field, different methods of production data analysis were used to understand the production performances. The recent advances in RTA allows us to apply the classical single well analysis method to a multiple well and multiple phase flow using Generalized Pseudo Pressure (GPP).
The previously published workflow by the authors (
Sow, Chia Shen (PETRONAS Carigali Sdn Bhd) | Bashir, Aamir (PETRONAS Carigali Sdn Bhd) | Chowdhury, Utpal (PETRONAS Carigali Sdn Bhd) | Hajizadeh, Alireza (PETRONAS Carigali Sdn Bhd) | Ridzuan, Ahmad Idriszuldin B (PETRONAS Carigali Sdn Bhd)
For E&P upstream player, the most exciting oil and gas development project is to transform a commercial hydrocarbon resources into readiness for production to meet the company investment portfolio. It involves field development planning, design, technology, procurement, construction, drilling and start-up prior to handover to production operations.
Most of the times, economic evaluation, assessment of risk and return on investiment (ROI) from the project are the key factors to determine the fate of the project during feasibility study and/or before the Final Investment Decision (FID) phase. Moreover the project cost, schedule, reserves to be developed and production profile are the key parameters to dictate the cash flow and net present value.
The general practice is that once the project completed, the reservoir model will be updated with new findings and surprises observed during drilling phase and include in post drilling evaluation report. After this stage, the project team will be disbanded and most companies will be lacking a single point of accountability for delivering production as promised
In this case study, the real time production and survelliance data were analysed. Although initial production did not meet the FDP delivery target due to project delays and subsea facilities downtime which causes production deferment, the stabilized production trends with time indicated a potential reserves gain by about 50%.
In summary, the analysis shows the value of analyzing the production and surveillance data by a dedicated team to assess the current field performance compared with the forecast profile from FDP study. The deviation can be a triggering point for revision on the resources figures, future infill opportunities and may contribute to the future cluster development within the same PSC.
Aftab, Muhammad Nadeem (Eastern Testing Services Pvt. Ltd.) | Qureshi, Imran (Eastern Testing Services Pvt. Ltd.) | Ashraf, Mohammad (Eastern Testing Services Pvt. Ltd.) | Bhayo, Sarfraz Ahmed (PETRONAS Carigali (Pakistan) Ltd.) | Bashir, Aamir (PETRONAS Carigali (Pakistan) Ltd.) | Ali, Abdul Salam (University of Engineering and Technology Lahore)
The productivity of the perforated wells is controlled by several perforating parameters; perforation length, perforation diameter, degree of the damage around the perforation tunnels, shot density, and perforation phasing angle. In a new well, once the well is perforated and the production is tested, the well is then killed and completed. Even with the used of nonaggressive kill fluid and non-damaging completion fluid, some degree of formation and perforations damages are induced during well killing and completion operations. Reduction of well productivity post completion compared to pre-completion is often observed.
The well productivity can be restored by stimulation treatment which is commonly successful practice in carbonate oil reservoirs but this option can be complicated when it comes to sandstone and gas reservoirs. Production enhancement through matrix stimulation on sandstone and gas wells has much lower success rate. This option is even more difficult in cases where reservoir information is limited. Restoring the gas well productivity to the initial pre-completion condition is challenging and most gas wells unable to deliver the expected production.
This paper describes a case history of a gas well in sandstone reservoir, where productivity falls dramatically after completion. Proper investigations were carried out through well test evaluations and comparisons to pre-completion tests which showed high degree of formation and perforation damages. Potential root causes from completion activities which contributed to the damages were identified. Several productivity enhancement options were evaluated in order to restore the well productivity. Re-perforation option was selected as the best option with lowest risk to induced further damage to the formation as well as being the most economical option available. Re-perforation was carried out on the same interval as the original perforations using reactive liner perforating technology. Reactive liner perforating technology was used as it is independent of rock properties and wellbore conditions.