Throughout the production life of a gas well its reservoir pressure declines and well becomes prone to liquid loading. The stationary liquid column in the wellbore exerts back pressure on the formation resulting in decrease or sometimes ceases the production. The overall outcome of this phenomenon is reduced recovery factor resulting in loss of reserves. Increasing Liquid Gas Ratio (LGR), decreasing gas rates and velocities with decreasing reservoir pressure are the main factors contributing in liquid loading. Various methods have been used in the industry to de-liquefy gas wells and maintain production rates. One method to de-liq a gas well is down hole soap injection through 1/4" or 3/8" capillary string to reduce the effective density and surface tension of the produced liquids. This method is cheap and effective, no external source of energy is needed since it utilizes reservoir energy. Injected soap or foam must be selected according to the reservoir characteristics. This paper shares the case studies of different wells having depleted reservoir pressures and liquid loading tendency. Foam Assisted Lift (FAL) was implemented on these wells as a de-liq technique, detailed study was carried out to observe their production behaviors and economic benefits from FAL. This work also incorporates the good and bad practices to ensure FAL is effectively de-liquefying a gas well to maximize production. The different practices proposed in this study can be used as an analogy to ascertain soap injection is performing in the best way to attain incremental production from depleted gas wells with liquid loading problems.
Liquid loading is an ineluctable problem encountered by gas wells as their reservoir pressure declines and Gas-Liquid Ratio (GLR) increases. Foam Assisted Lift (FAL) is one of the modern methods for dewatering gas wells by reducing effective density and surface tension of produced fluid. Gas lift is also a widely used method that reduces flowing bottom-hole pressure by injecting gas in the well to lower hydrostatic head. This paper proposes a combination of above mentioned technologies called Foam Assisted Gas Lift (FAGL) and recommends its' efficiency over two specific scenarios; a) when reservoir pressure is low and static liquid level remains below bottommost SPM, b) when there is a considerable liquid column in wellbore and gas injection pressures are limited due to surface constraints, injecting foam decreases the hydrostatic head and requires less gas injection pressure to offload the well. In either case, FAL can offload the well but the stabilized rates achieved are uneconomical compared to the soap requirement per day. FAGL is applied on mature wells having low reservoir pressures and completed with single SPM. These wells had frequent load-up issues and FAL/gas-lift failed due to low reservoir inflow. After FAGL is implemented, frequent load-up issues have been resolved and wells began to produce at increased stabilized rates. FAGL also emerged as an economical option because it reduced the soap /injected gas requirement per day and increased gas rates and overall recovery. For wells with deep SPMs, depleted reservoir pressure and liquid loading problems, FAGL could be an economical de-liquefaction method when compared to standalone gas-lift or FAL due to its lower OPEX.
Liquid loading is an ineluctable problem encountered by gas wells as their reservoir pressure declines and Gas-Liquid Ratio (GLR) increases. Foam Assisted Lift (FAL) is one of the modern methods for dewatering gas wells by reducing effective density and surface tension of produced fluid. Gas lift is also a widely used method that reduces flowing bottom-hole pressure by injecting gas in the well to lower hydrostatic head. This paper proposes a combination of above mentioned technologies called Foam Assisted Gas Lift (FAGL) and recommends its’ efficiency over two specific scenarios; a) when reservoir pressure is low and static liquid level remains below bottommost SPM, b) when there is a considerable liquid column in wellbore and gas injection pressures are limited due to surface constraints, injecting foam decreases the hydrostatic head and requires less gas injection pressure to offload the well. In either case, FAL can offload the well but the stabilized rates achieved are uneconomical compared to the soap requirement per day. FAGL is applied on mature wells having low reservoir pressures and completed with single SPM. These wells had frequent load-up issues and FAL/gas-lift failed due to low reservoir inflow. After FAGL is implemented, frequent load-up issues have been resolved and wells began to produce at increased stabilized rates. FAGL also emerged as an economical option because it reduced the soap/injected gas requirement per day and increased gas rates and overall recovery. For wells with deep SPMs, depleted reservoir pressure and liquid loading problems, FAGL could be an economical de-liquefaction method when compared to standalone gas-lift or FAL due to its lower OPEX.
Salt precipitation and accumulation in the wellbore is a common phenomenon witnessed in the twilight of gas wells; gas expansion, water evaporation, abrupt changes in pressure and temperature etc. are the main driving forces for its occurrence. Low reservoir pressures helps in water vaporization when quantity of water in gas phase is not high. Reduction in pressure thus causes water vaporization and hence salt accumulation. The salt precipitation results in obstruction of gas flow in purlieu of wellbore, if the problem is not rectified timely it might cease the wellbore completely resulting in complete loss of production. To restore production frequent wellbore cleanout jobs are required, these cleanout jobs are usually carried out through coiled tubing unit and different liquids are utilize ranging from fresh water, nitrified brine, organic acids etc. These all treatments are expensive and effect well economics. Few wells in United Energy Pakistan Limited (UEP) were facing salt precipitation problem and not flowing up to their potential rates, regular wellbore clean out jobs carried out but their impressions were not long lasting and salt again accumulated. In this paper, removal of salt deposition through regular deployment salt sticks on two wells K-1 and T-1 are discussed. In these wells salt sticks are used at different frequencies to overcome salt deposition. Post job results showed improvement in gas rates, gauge cutter runs also confirmed salt deposition is minimized and production is stabilized.
A workflow is presented in this study named Fracture Evaluation & Design System (FEDS) that couples established technique of nodal analysis (well performance evaluation) and Quasi-3D (type of Pseudo-3D) hydraulic frac models. This methodology of hydraulic frac simulation is more robust in predicting post-frac production rates from fractured wells specifically in unconventional reservoirs like shales and has several advantages over utilizing frac models in isolation. The results from FEDS are compared with commercial frac simulators and discrepancies are noted. This workflow is divided in two segments, flow in frac (or reservoir) and flow in wellbore. The frac element is calculated through Quasi-3D frac model, a published hydraulic frac model that calculates frac geometry (frac length, width & height) in asymmetric multilayer formations such as Pakistan's Shales. This calculation is used to estimate the dimensionless fracture conductivity (FcD) which is a measure of effectiveness of the frac. These calculations are combined with reservoir parameters such as pressure, permeability and skin to generate deliverability profile or Inflow Performance Relationship (IPR). This IPR generated from calculated fracture geometry & conductivity inherently accounts for uncertainty of formation stresses, frac height implications, effect of permeability variation etc. This is a numerically calculated IPR, while fracture growth is being modelled; IPR is constantly updated based on fracture model results in a fully coupled setting. Second element of wellbore hydraulics or Vertical Lift Performance (VLP) is calculated using several published correlations such as Gray et al. The idea behind incorporating VLP in frac simulation is to model effects of water holdup, slippage, multiphase flow etc. Most commercial frac simulators utilize correlations of FcD to estimate post frac production, such as cinco-ley et al correlation. However, often production at surface is hampered due to wellbore effects such as water slippage. This is one of the major reason, despite having reliable input data, design post frac profile is much higher than realized production. The working of this workflow is validated by applying on two field fracture treatments. One of this treatment is in conventional sandstone reservoir while other is unconventional. The design & post frac production prediction is conducted in published frac models (that are used by commercial simulators) and using Quasi-3D frac model in FEDS. In all cases, production predicted by FEDS is significantly lower than commercial simulators. Main frac treatment is conducted as per design in these two reservoirs and actual post frac production is measured. The instantaneous gas production from both reservoirs is in better agreement with production predicted by FEDS validating the calculations of this workflow. This workflow brings together two well established techniques of petroleum engineering to evaluate effectivity of fracture treatments in the system as a whole. The modular nature of this system allows the utility of any vertical lift correlations, even calibrated or mechanistic models that best replicate the well in question. Further, with system optimization option available, several sensitivities can be readily run to evaluate range of uncertainty in post-frac production.
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