A Robust Model for Integration of Sand-Arch Stability and Fractal Wormhole Network in CHOPS and post-CHOPS Process Simulation
Creators: Qin, Yadong
Publisher: name: University of Alberta Library
Year: 2024

<p>Cold heavy-oil production with sand (CHOPS) is a primary recovery process in unconsolidated heavy-oil reservoirs. The recovery factor typically ranges from 5% to 15% of the initial oil in place (OOIP). Approximately 90% of crude oil is left underground with considerable exploitation potential after the CHOPS process. Existing CHOPS simulation models capture many of the key characteristics of CHOPS mechanisms, including foamy oil flow, growth of the wormhole network, and sand production. However, the simulation models are only tested based on the performance of a single CHOPS well; their ability to represent a variety of CHOPS production profiles is rarely examined. This thesis addresses this issue. It provides an improved CHOPS simulation model that is tested against several CHOPS wells with different production profiles. This expands the range of CHOPS wells that can be represented with this improved CHOPS simulation model. As a result, a wider range of reservoir conditions at the end of CHOPS is simulated, enhancing the set of initial conditions available for simulating subsequent post-CHOPS processes. <br>
An improved set of initial conditions for simulating the performance of potential post-CHOPS recovery technologies, such as cyclic solvent processes, would enable the effect of these conditions to be examined in more detail. For example, the impact of the wormhole network distribution on the uncertainties in post-CHOPS performance could be quantified more readily. This thesis extends the CHOPS simulation model developed in a previous study (Yu and Leung, 2020), incorporating dynamic fractal wormhole growth, sand production, and multi-component foamy oil flow. Appropriate modifications have been made to this model to ensure that the simulated production performance, including the oil and sand production profiles, bottom-hole pressure (BHP), and producing gas-oil ratio (GOR), is reasonable and sufficiently flexible to capture a wide range of CHOPS production profiles. <br>
A field case study was carried out to examine the effectiveness of this improved CHOPS simulation model to capture a variety of CHOPS production profiles. Three CHOPS wells from Dee Valley with different production profiles were simulated. This involved the detailed examination of the relevant model parameters for improved matching against field data, including incorporating a representation of the wormhole network growth rate and density that depended on the oil and sand production profiles. This included the incorporation of different fractal patterns to represent different wormhole network characteristics. As well, the sand production model in the study by Yu and Leung (2020) was adjusted to capture the characteristics typical of the entire sand production profile from CHOPS wells: i.e., a rapid increase in the rate of sand production to a peak, and subsequent decline to a low but persistent level. Similarly, the foamy oil model in the study by Yu and Leung (2020) was refined in order to capture the characteristics typical of gas production from CHOPS wells: a period of relatively low but constant producing GOR followed by a sharp increase in producing GOR as a well ages.<br>
Simulations of a promising post-CHOPS technology, cyclic solvent injection (CSI), were carried out to study the performance of this recovery technology to enhance heavy oil recovery after the CHOPS process. The reservoir conditions at the end of CHOPS from several wells in the CHOPS simulation studies were used to determine the initial conditions for the CSI simulations. For these simulations, pure CO2 was selected as the solvent to repressurize the reservoir and stimulate further oil production. The simulations explored various mechanisms involved in the dissolution of CO2 into heavy oil during injection and exsolution of CO2 from heavy oil during production. In particular, these simulations focused on the nonequilibrium aspects of CO2 dissolution and exsolution. The simulation results indicated that foamy oil flow (in the form of dispersed bubbles) is beneficial to oil production. </p>