1.  Investigation of Multiphase Flow Behavior in Horizontal Wells

1.  Investigation of Multiphase Flow Behavior in Horizontal Wells


Multiphase flow is inevitably encountered in both gas and oil wells. Gas wells will have water and condensate below the dew point as the liquid phase, while oil wells will present a vapor phase as pressure goes below the bubble point pressure.  Solids can also be encountered, creating additional challenges.   The available knowledge of multiphase flow behavior in horizontal wells is limited.  This research area aims to further the knowledge of multiphase flow behavior in horizontal wells, providing guidance for proper well design and operation.

     1.1 Solid Transport in Horizontal Wells

1.1 Solid transport in horizontal wells

The project that has been initiated in Fall 2019.  Over the life of an oil and gas reservoir, it is likely to encounter sand production. Sand can accumulate in horizontal wells under certain operating conditions and eventually may lead to a blockage or restriction of the flow.  Thus, the management of such systems requires knowledge on how sand is transported, when and where it accumulates, and, if possible, how sand beds can be removed.  The main objective is to investigate experimentally and theoretically the sand transport in liquid and gas-liquid flows for various well configurations, namely toe-up, sump, and horizontal.  Practical operating envelopes will be developed to estimate liquid and gas velocities required to transport sand slugs.

Preliminary gas-liquid-sand flow tests were conducted for a constant liquid flow rate.  Results show that sand transport occurs with high gas flow rates.  The reduction in gas flow rate reduces the liquid velocity promoting the accumulation of sand in the lateral.  As the gas flow rate reaches the severe slugging region, the sand is pushed through the vertical section, and most of the sand returns to the bottom of the lateral after the blowout.

2.  Investigation of Artificial Lift Techniques in Horizontal Wells

2.  Investigation of Artificial Lift Techniques in Horizontal Wells


Horizontal wells provide unique challenges for the traditional Artificial Lift (AL) systems. Typically, AL systems have been designed and optimized for vertical and deviated configurations. Horizontal well geometry is prone to flow instabilities, such as severe slugging and terrain-induced slugging, demanding the AL system to operate under harsh conditions. Emphasis on the interaction between the dynamics of the horizontal well flow and various artificial lift methods is provided, as described below.

     2.1  Plunger Lift Studies

2.1  Plunger Lift Studies


Plunger lift systems are widely used as a dewatering method for gas wells.  This artificial lift method has many advantages that make it an attractive solution to liquid loading, including very low investment and operational costs, no external energy requirement, increased production, and prevention of paraffin, wax, and scale deposition.  There are two main types of plunger lift: continuous and conventional.  Conventional plunger provides an intermittent production for the late-life of the well, whereas continuous flow plunger, which is deployed during the early stages of liquid loading, facilitates continuous production.  Typically, standalone plunger wells are completed without packers.  However, a combination of plunger lift and intermittent or continuous gas-lift may require its deployment in packered completions.

The current plunger lift studies of TUHWALP are divided into two categories, namely, the study of the conventional plungers for horizontal wells and the plunger assisted gas lift (PAGL).

          2.1.1  Study of Conventional plunger Lift in Horizontal Wells 

2.1.1  Study of Conventional Plunger Lifrt in Horizontal Wells


The design of a conventional plunger lift system consists of selecting a plunger type, determining a bumper spring setting depth, and estimation of the controller set points to cycle a motor valve.  The motivation for the project lies in the fact that there is no design software capable of performing the aforementioned calculations.  Consequently, the objective of this project is to develop a comprehensive software to simulate a conventional plunger lift and gas-assisted plunger lift (GAPL) systems.  A detailed study of plunger upward and downward movement is being conducted to achieve this objective.  The expected deliverables include a new set of high-resolution experimental data for different plunger types and stages of plunger lift and a model describing the behavior.  The acquired knowledge will be deployed in a software package capable of providing design parameters for plunger deployment, machine learning methodology to analyze routine plunger lift data and optimize the cycles.

2.1.2  Continuous Flow Plunger and Plunger Assisted Gas Lift (PAGL)

2.1.2  Continuous Flow Plunger and Plunger Assisted Gas Lift (PAGL)


Plunger operates in a continuous fashion to deliquefy gas wells. Continuous flow plungers can fall against high gas flow rates, making them suitable for operations at higher gas and liquid flow rates.  It does not require a shut-in period to build up pressure, and the plunger completes its cycle without any intervention.  It can also be combined with a gas lift application, which is called Plunger Assisted Gas Lift (PAGL).  Switching from gas lift to PAGL allows operators to reduce gas injection amount significantly while maintaining or increasing the production.  This method provides to operate under initial liquid loading conditions while preventing liquid accumulation at the bottomhole.  Also, it helps to remediate paraffin deposition.  As PAGL method gets traction in the industry, TUHWALP members are highly interested in a systematic study of it.  Instead of relying on rules of thumb, guidelines supported by systematic research and analytical solutions are needed.  The objectives are to find optimum gas injection rates, define operational boundaries, optimize the plunger cycle, and propose guidelines for plunger selection.

     2.2  Dounhole Separation for Horizontal Wells

2.2  Downhole Separatio for Horizontal Wells


Downhole separation has been traditionally used to enable the application of pumping systems in high GOR wells.  A pre-requisite for any pumping system is efficient gas separation.  Separation studies should be an initial step in any artificial lift method requiring pumping.  Therefore, TUHWALP began a research effort to optimize current downhole separators for horizontal well conditions.  The acquired knowledge will be deployed in new guidelines for downhole separator design and a computational tool to define the dimensions and position for operating conditions.

          2.2.1  Gas-Liquid Downhole Separation for Deviated or Horizontal Wells

2.2.1  Gas-Liquid Downhole Separator for Deviated ro horizontal Wells


Up to this date, the industry uses simple “rules-of-thumb, which are developed based on field observations and experiments with vertical wells and separators below or at the perforations” to design a separation installation.  This project evaluates the performance of a shroud type gravity-driven downhole separator under the current challenges of pumped wells, e.g., horizontal well geometry, high GOR, and upstream flow effect such as slugging.  The shroud type separators are uncomplicated, yet robust, and the most well-known and applied in the field.  These qualities make this evaluation mandatory for downhole separator comparison.  The project aims to test the performance of the separator under numerous operating conditions, deviation angles, separator geometries, and upstream flow characteristics.  The expected deliverables include a new evaluation method for downhole separators, which is currently not available— and a new set of high-resolution experimental data for different separator geometries under numerous operational conditions.  The acquired knowledge will be deployed as a software package capable of providing design parameters for separators, evaluate current separator designs, and provide operating envelopes.  

          2.2.2  Detailed Investigation of Downhole Separation Mechanism

2.2.2  Detailed Investigation of Downhole Separation Mechanism


The evidence collected in the previous project revealed the lack of knowledge related to the physics of the separation in downhole separators. Therefore, this project consists of a detailed investigation of the gas-liquid separation mechanisms presented at the inlet of a gravity-driven downhole separator.  For this purpose, novel computing visual algorithms and Computational Fluid Dynamics (CFD) simulations are being used.  The effect of the gas bubble and liquid interaction, gas bubble size distribution, and separator geometry are being evaluated.  The results will be used to propose mathematical guidelines and physics-based criteria for the evaluation and design of downhole separators.

          2.2.3  Downhole Separator Pump Interaction

2.2.3  Downhole Separator-Pump Interaction


Given that downhole separators are considered as a pre-requisite for any artificial lift method based on pumping, the evaluation of the interaction of separator and pump is a requirement. Consequently, this project aims to evaluate the effect of different pumping systems in the performance of the downhole separator.  Sucker rods and ESP mock-up pumps will be used to evaluate the performance of their working principle on the separator.  The results of this study will provide guidelines on how to operate the artificial lift system without damaging or adverse effects on the separation performance and the efficacy of the artificial lift method.  Finally, it will provide operating maps for separator-pumps assemblies.

          2.2.4  Evaluation of Current Separation Technology for Horizontal Wells 

2.2.4  Evaluation of Current Separation Technology for Horizontal Wells


Current downhole separator technology has been developed and optimized for vertical well configurations.  The main objective of this project is the evaluation of downhole separation technology in the horizontal well configuration.  The results of this project will be used to generate guidelines to select downhole separators for horizontal wells.  The results will also be used to improve the prediction capability of the TUHWALP downhole separation software.

     2.3  Experimental and Modeling Study of ISP Deployed in the Lateral

2.3  Experimental and Modeling Study of ESP Deployed in the Lateral


Electrical submersible pumping (ESP) is considered the second most widely used artificial lift method in oil production in terms of the number of installations.  It is the most used method when it comes to the amount of produced liquid.  Although ESPs were initially developed to be deployed in vertical and slightly deviated wells, currently, a significant number of ESPs are operating in the lateral of horizontal wells.  The combination of advances in drilling technology and the necessity of enhanced production from shale reservoirs resulted in an increase in horizontal wells, which may benefit from the ESP as an effective method for lifting fluids.

The objective of this project is the experimental investigation of the performance of an electrical submersible pump (ESP) deployed in horizontal and near-horizontal orientation, emulating the lateral section of a horizontal well.  Models will be developed for predicting the performance of the ESP operating under segregated and intermittent flow patterns.

3.  Artificial Lift and Reservoir Interaction

3.  Artificial Lift and ReservoirUnconventional reservoirs are characterized by low permeability, resulting in production under the transient flow regime for an extended period.  Consequently, conventional nodal analysis, with the implicit assumption of pseudo-steady state flow, is not applicable for predicting future production.  The objective of this research line is to develop computational tools to predict the performance of a producing well from an unconventional reservoir.  The tool allows the inclusion of different artificial lift technologies and evaluates its impact on the well production.  By using the tool, it is also possible to evaluate the impact on reservoir performance due to modifications in the operating conditions resulting from valves opening/closing and changes in tubing/casing internal diameter (ID).  Different transient flow regimes (such as linear flow, radial flow, bilinear flow, etc.) will be considered as the production evolves with time.  The tool will be developed as a plug-in for expanding the capabilities of commercial simulators.  This research line also includes: (a) development of a transient inflow performance relationship (IPR) methodology, (b) implementation of correlations to detect liquid loading in wells, and (c) a tool to support in the selection of the best artificial lift technology over the well lifetime.