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Summary Decline curve analysis (DCA) has been the mainstay in unconventional reservoir evaluation. Because of the extremely low matrix permeability, each well is evaluated economically for ultimate recovery as if it were its own reservoir. Classification and normalization of well potential is difficult because of ever-changing stimulation total contact area and a hyperbolic curve fit parameter that is disconnected from any traditional reservoir characterization descriptor. A new discrete fracture model approach allows direct modeling of inflow performance in terms of fracture geometry, drainage volume shape, and matrix permeability. Running such a model with variable geometrical input to match the data in lieu of standard regression techniques allows extraction of a meaningful parameter set for reservoir characterization, an expected outcome from all conventional well testing. Because the entirety of unconventional well operation is in transient mode, the discrete fractured well solution to the diffusivity equation is used to model temporal well performance. The analytical solution to the diffusivity equation for a line source or a 2D fracture operating under constrained bottomhole pressure consists of a sum of terms, each with exponential damping with time. Each of these terms has a relationship with the constant rate, semisteady-state solution for inflow, although the well is not operated with constant rate, nor will this flow regime ever be realized. The new model is compared with known literature models, and sensitivity analyses are presented for variable geometry to illustrate the depiction of different time regimes naturally falling out of the unified diffusivity equation solution for discrete fractures. We demonstrate that apparent hyperbolic character transitioning to exponential decline can be modeled directly with this new methodology without the need to define any crossover point. The mathematical solution to the physical problem captures the rate transient functionality and any and all transitions. Each exponential term in the model is related to the various possible interferences that may develop, each occurring at a different time, thus yielding geometrical information about the drainage pattern or development of fracture interference within the context of ultralow matrix permeability. Previous results analyzed by traditional DCA can be reinterpreted with this model to yield an alternate set of descriptors. The approach can be used to characterize the efficacy of evolving stimulation practices in terms of geometry within the same field and thus contribute to the current type curve analyses subject to binning. It enables the possibility of intermixing of vertical and horizontal well performance information as simply gathering systems of different geometry operating in the same reservoir. The new method will assist in reservoir characterization and evaluation of evolving stimulation technologies in the same field and allow classification of new type curves.
Abstract The objective of this study was to improve the accuracy of condensate gas ratio (CGR) prediction in the Pailin and Moragot areas. Conventional method to predict liquid component reserves used only long-life condensate gas ratio (long-life CGR) from near-by production platform(s). The long-life CGR data are available in the mature production platforms which commonly takes 1-2 years to observe the decline trend so that there is no available data in the new drilled area and non-production area. This might cause inaccurate prediction of liquid reserves in the future platform especially in the platform locates far away from the mature production area. Multiple data which are basin modeling, geochemical data, drill-stem test, and batch-level production were analyzed and integrated to improve the accuracy of CGR prediction and understand geological reasons of high or low liquid production platform. These data can improve the confident level for CGR estimation in the non-production area and help identify potentially high liquid production platforms. The results show that the high liquid production in Pailin and Moragot fields related with the differentiation of source rock and migration process. There are three (3) separated trends in Pailin field and two (2) trends in Moragot field using geochemical data and basin modeling data. The local DST data has been integrated to confirm the extent of potentially high liquid production in several future platforms which locates in non-production area. Also, the updated production data has been re-visited to estimate the new CGR for the project located near-by production platform.
Karpaya, Shaturrvetan (PETRONAS Carigali Sdn.Bhd.) | Sidek, Sulaiman (PETRONAS Carigali Sdn.Bhd.) | Ab Ghani, Dani Angga (PETRONAS Carigali Sdn.Bhd.) | Ab Rahman, Hazrina (PETRONAS Carigali Sdn.Bhd.) | Yong, Aivin (KROHNE EMAS Sdn.Bhd.) | Subbarayan, Venukumaran (KROHNE EMAS Sdn.Bhd.) | Chew, Simon (Petrotechnical Inspection (M) Sdn.Bhd.)
Abstract Installation of Wet Gas Metering System (WGMS) on a platform for the purposes of real-time measurement of liquid and gas production rates as well as performance monitoring as part of reservoir and production optimization management are quite common nowadays in Malaysia. Nonetheless, understanding of wells production deliverability invariably measured using these Wet Gas Meter (WGM) which provides the notion of production rates contributed by the wells are paramount important, eventually the produced fluids will be processed by various surface equipment at the central processing platform before being transport to onshore facilities. However, the traditional WGM are known to operate within ±10% accuracy, whereby the confidence level on measurement of the produced fluids can be improved either by updating with accurate PVT flash table or combination of results from performing tracer dilution technique for data verification. Sarawak Gas Field contains a number of gas fields offshore East Malaysia, predominantly are carbonate type formation, where one (1) of the field operated by PETRONAS Carigali Sdn.Bhd.(PCSB) is a high temperature accumulation at which temperature at the Gas Water Contact (GWC) approximately 185°C and full wellstream Flowing Tubing Head Temperature (FTHT) records at 157°C. Cumulative field production of five (5) wells readings from WGM had shown 9.1% differences as compared to the export meter gas readings. As part of a strategy to provide maximum operational flexibility, improvement on accuracy of the WGM is required given that the wells have higher Technical Potential (TP) but are limited by threshold of the multi-stage surface processing capacity. This also impacts commerciality of the field to regaining the cost of capital investment and generate additional revenue especially when there is a surge in network gas demand, as the field unable to swiftly ramp-up its production to fulfill higher gas demand considering the reported production figures from cumulative WGM surpassing the surface equipment Safe Operating Envelope (SOE). Our approach begins with mass balance check at the WGMS and export meter including the fuel, flare and Produced Water Discharge (PWD) to check mass conservation by phases because regardless different type of phases change occurs at topside the total mass should be conserved (i.e. for total phases of gas, condensate and water) provided that precise measurement by the metering equipment. Tracer dilution measurement of gas, condensate and water flowrates were used to verify the latest calibrated Water Gas Ratio (WGR) and Condensate Gas Ratio (CGR) readings input into the WGM. Consequently, PVT separator samples were also taken via mini-separator for compositional analysis (both gas and condensate) and for mathematical recombination at the multi-rates CGR readings to generate a representative PVT compositional table. Simultaneously, process model simulation run was conducted using full wellstream PVT input to validate total field production at the export point. This paper presents practical approach to balance the account, to ensure the SOE at topside as well as to improve the PVT composition at the WGM for high temperature field that emphasizes on understanding of compositional variations across production network causing significant differences in total field production between WGM and the allocation meter.
Tang, Catherine, Ye (Petronas Carigali Sdn Bhd) | Tan, Kok Liang (Petronas Carigali Sdn Bhd) | Riyanto, Latief (Petronas Carigali Sdn Bhd) | Tusimin, Fuziana (Petronas Carigali Sdn Bhd) | Sapian, Nik Fazril (Petronas Carigali Sdn Bhd) | Sharim, Noor Azima (Petronas Carigali Sdn Bhd)
Abstract Well#1 was completed as horizontal oil producer with Openhole Stand-Alone Sandscreens (OHSAS) across a thin reservoir with average thickness of 20ft in Field B. The first Autonomous Inflow Control Device (AICD) in PETRONAS was installed to ensure balanced contribution across horizontal zones with permeability contrasts and to prevent early water and gas breakthrough. Integrated real-time reservoir mapping-while-drilling technology for well placement optimization combined with industry-leading inflow control simulator for AICD placement were opted. The early well tests post drilling showed promising results with production rate doubled the expected rate with no sand production, low water cut and lower Gas to Oil Ratio (GOR). Reservoir Management Plan (RMP) for this oil rim requires continuous gas injection into gas cap and water injection into aquifer. However, due to low gas injection uptime caused by prolonged injection facilities constraints, the well's watercut continued to increase steadily from 0% to 80% within a year of production despite prudent surveillance and controlling of production during injector's downtime. After the gas injection performance has improved, the well was beaned up as part of oil rim management for withdrawal balancing. Unfortunately, a month later, the production rate showed a sudden spike with significantly low wellhead pressure, followed by hairline leak on its choke valve and leak at Crude Oil Transfer Pump (COTP) recycle line. Sand analysis by particle size distribution (PSD) confirmed OHSAS failure, while the high gas rate from well test results confirmed AICD failure. A multidisciplinary investigation team was immediately formed to determine the root cause of the failure event. Root Cause Failure Analysis (RCFA) method was opted to determine the causes of failures, including the reanalyzing of the OHSAS and AICD completion design. The well operating strategy was also reviewed thoroughly by utilizing the well parameters trending provided in the Exceptional Based Surveillance (EBS) Process Information (PI) ProcessBook. Thorough RCFA concluded that frequent platform interruptions and improper well start-up practices have created abrupt pressure changes in the wellbore, which has likely destabilized the natural sand pack around the OHSAS and created frequent burst of sand influx across AICDs. The operating of a high gas-oil ratio (GOR) and high watercut sand prone well without pre-determined AICD sand erosion toleration envelope have also likely contributed to the failure of AICDs. The delay in detection of OHSAS failure in Well#1 due to ineffective sand monitoring method thus resulted in severe sand production which caused severe leak at its choke valve and COTP recycle line.
Mohsin, Adel (College of Science and Engineering, Hamad Bin Khalifa University) | Abd, Abdul Salam (College of Science and Engineering, Hamad Bin Khalifa University) | Abushaikha, Ahmad (College of Science and Engineering, Hamad Bin Khalifa University)
Abstract Condensate banking in natural gas reservoirs can hinder the productivity of production wells dramatically due to the multiphase flow behaviour around the wellbore. This phenomenon takes place when the reservoir pressure drops below the dew point pressure. In this work, we model this occurrence and investigate how the injection of CO2 can enhance the well productivity using novel discretization and linearization schemes such as mimetic finite difference and operator-based linearization from an in-house built compositional reservoir simulator. The injection of CO2 as an enhanced recovery technique is chosen to assess its value as a potential remedy to reduce carbon emissions associated with natural gas production. First, we model a base case with a single producer where we show the deposition of condensate banking around the well and the decline of pressure and production with time. In another case, we inject CO2 into the reservoir as an enhanced gas recovery mechanism. In both cases, we use fully tensor permeability and unstructured tetrahedral grids using mimetic finite difference (MFD) method. The results of the simulation show that the gas and condensate production rates drop after a certain production plateau, specifically the drop in the condensate rate by up to 46%. The introduction of a CO2 injector yields a positive impact on the productivity and pressure decline of the well, delaying the plateau by up to 1.5 years. It also improves the productivity index by above 35% on both the gas and condensate performance, thus reducing production rate loss on both gas and condensate by over 8% and the pressure, while in terms of pressure and drawdown, an improvement of 2.9 to 19.6% is observed per year.
Soroush, Mohammad (University of Alberta and RGL Reservoir Management Inc.) | Roostaei, Morteza (RGL Reservoir Management Inc.) | Hosseini, Seyed Abolhassan (University of Alberta and RGL Reservoir Management Inc.) | Mohammadtabar, Mohammad (University of Alberta and RGL Reservoir Management Inc.) | Pourafshary, Peyman (Nazarbayev University) | Mahmoudi, Mahdi (RGL Reservoir Management Inc.) | Ghalambor, Ali (Oil Center Research International) | Fattahpour, Vahidoddin (RGL Reservoir Management Inc.)
Summary Kazakhstan owns one of the largest global oil reserves (approximately 3%). This paper aims at investigating the challenges and potentials for production from weakly consolidated and unconsolidated oil sandstone reserves in Kazakhstan. We used the published information in the literature, especially those including comparative studies between Kazakhstan and North America. Weakly consolidated and unconsolidated oil reserves in Kazakhstan were studied in terms of the depth, pay‐zone thickness, viscosity, particle‐size distribution (PSD), clay content, porosity, permeability, gas cap, bottomwater, mineralogy, solution gas, oil saturation, and homogeneity of the pay zone. The previous and current experiences in developing these reserves were outlined. The stress condition was also discussed. Furthermore, the geological condition, including the existing structures, layers, and formations, were addressed for different reserves. Weakly consolidated heavy‐oil reserves in shallow depths (less than 500‐m true vertical depth) with oil viscosity of approximately 500 cp and thin pay zones (less than 10 m) have been successfully produced using cold methods; however, thicker zones could be produced using thermal options. Sand management is the main challenge in cold operations, while sand control is the main challenge in thermal operations. Tectonic history is more critical compared with the similar cases in North America. The complicated tectonic history necessitates geomechanical models to strategize the sand control, especially in cased and perforated completions. These models are usually avoided in North America because of the less‐problematic conditions. Further investigation has shown that inflow‐control devices (ICDs) could be used to limit the water breakthrough, because water coning is a common problem that begins and intensifies the sanding. This paper provides a review on challenges and potentials for sand control and sand management in heavy‐oil reserves of Kazakhstan, which could be used as a guideline for service companies and operators. This paper could be also used as an initial step for further investigations regarding the sand control and sand management in Kazakhstan.
Pseudo-steady state (or pseudo steady-state), is also referred to as "stabilized," or as "steady state in a bounded drainage area." This type of reservoir flow occurs much more frequently than steady-state flow or unsteady-state flow with an expanding drainage radius. Pseudo-steady state (PSS) flow occurs during the late time region when the outer boundaries of the reservoir are all no flow boundaries. This includes not only the case when the reservoir boundaries are sealing faults, but also when nearby producing wells cause no flow boundaries to arise. During the PSS flow regime, the reservoir behaves as a tank.
This page discusses various aspects of gas reservoir performance, primarily to determine initial gas in place and how much is recoverable. The equations developed can used to form the basis of forecasting future production rates by capturing the relationship between cumulative fluid production and average reservoir pressure. Material-balance equations provide a relationship between original fluids in place, cumulative fluid production, and average reservoir pressure. This equation is the basis for the p/z-vs.-Gp Reservoir engineers have often used pressure contour maps or some approximate methods to determine field average reservoir pressure for p/z analysis. Usually, however, individual well pressures are based on extrapolation of pressure buildup tests or from long shut-in periods. In either case, the average pressure measured does not represent a point value, but rather is the average value within the well's effective drainage volume (see Estimating drainage shapes).