Evaluation of post-CHOPS (Cold Heavy Oil Production with Sands) Enhanced Oil Recovery Methods

• Author / Creator

  Rangrizshokri, Alireza

• Due to its lower cost, the cold heavy oil production with sands (CHOPS) method is a common primary production recovery technique, not only in Canada where it originated, but also in many other countries including Venezuela, Kuwait, Russia, and China. However, this method has several practical limitations. It continuously changes the geomechanical and petro-physical properties of the reservoir due to the sand produced, resulting in high permeability channels known as wormholes. In addition, this method has a low oil recovery factor (5-15 %) and this entails further recovery techniques.
  Thermal methods after CHOPS are not usually favourable due to heterogeneity and reservoir instability. In addition, CHOPS wells are not completed for thermal (steam) operations. The CHOPS method is typically applied in thin formations in which heating by injected steam is characteristically inefficient. Solvent injection possesses similar problems caused by heterogeneity and cost. An option could be the hybrid application of steam/solvent. Assessment of this technique first requires a realistic modeling of the CHOPS process. Due to dynamic changes in reservoir properties, no valid model was available to accurately simulate field-scale CHOPS production.
  Therefore, a part of this thesis presents a quick workflow for CHOPS modeling to investigate efficient EOR/IOR (Enhanced/Improved Oil Recovery) methods after CHOPS. To achieve this, we first propose a partial-dual porosity approach coupled with algorithms for wormhole generation to create realistic static reservoir models. After generating fractal wormhole patterns of different kinds using a diffusion limited aggregation (DLA) algorithm, they were introduced into a reservoir model. Based on fractal analysis, novel upgridding procedures for wormhole network in partial-dual porosity models were introduced. After validation of the models using data obtained from a field in Alberta, several preliminary post-CHOPS scenarios including thermal, solvent, and thermal/solvent hybrid applications were simulated. In addition, a 3D geomechanical model was used to calculate the stress distribution in the history matched field. The hydro-geomechanical model was then used for field development planning, reservoir management and assessment of near wellbore regions during cyclic injection and production. The field-wide deformation and stress changes were analyzed in deep overburden, cap rock, and reservoir to show the influence of local stress orientations in soft and stiff layers.
  Next, an experimental set-up consisting of a sand-pack with different configurations of complexity of wormhole patterns was designed. The experiment was aimed to mimic cyclic solvent stimulation at reservoir conditions. The sand-pack experiments were numerically simulated and effective diffusion coefficients were obtained. To generate accurate predictions in field-scale simulation, an up-scaling procedure from laboratory results of the cyclic solvent injection process was suggested. The overall findings suggest that an improved heavy oil recovery could be achieved using combined light and heavy solvents in CHOPS reservoirs. Steam (or hot-water) was found to play a positive role in solvent retrieval. Finally, an uncertainty screening procedure was performed to assess the feasibility of cyclic solvent stimulation as a post-CHOPS method. An economics model was developed and after-tax NPV (Net Present Value) of the field at the end of cyclic solvent stimulation process was calculated. Such calculations have the priority to oil recovery factor or cumulative oil production as it could incorporate costs and sales simultaneously by performing continuous discounting and allow the asset holder to maximize NPVs and select the best development strategy.

• Subjects / Keywords

  • Upscaling
  • Fractal wormhole
  • Steam injection
  • Cyclic solvent injection
  • Post-CHOPS EOR
  • CHOPS modeling
  • Field scale application

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HX15Z95

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.