Complementary Workflows for Analyzing Multiphase Flowback and Post-flowback Production Data In Unconventional Reservoirs

• Author / Creator

  Ezulike, Obinna D

• The application of horizontal drilling and hydraulic fracturing techniques has resulted in the economic production of previously inaccessible hydrocarbon trapped in very-low permeability reservoirs such as Shale gas/oil, tight gas and tight oil. Although the economic production of these reservoirs supplement the decreasing hydrocarbon supply from conventional reservoirs to meet the world’s growing energy demand, modeling fluid flow in such complex reservoirs to minimize environmental pollution remains challenging. There have been improvements in the quality and frequency of rate and pressure measurements during fluid production from multi-stage fractured wells and in the ability of existing transient models to interpret multiphase flowback and post-flowback production data. However, the existing models either make many simplistic assumptions or are too complex. The simplistic nature of some of these models could result in overestimation or underestimation of reservoir parameters and hydrocarbon forecasts. The complexity of some of these models introduces high uncertainty in the estimates of resulting parameters such as fracture pore-volume, half-length and permeability. This study presents complementary workflows for the qualitative and quantitative analysis of flowback and post-flowback production data. The data are obtained from multifractured horizontal wells completed in low permeability reservoirs with a significant amount of reactivated natural fractures. The workflows are based on three key models proposed in the study, namely – flowback tank model, flowback analysis model and quadrilinear flow model. The main results from this work are summarized in the following paragraphs. The occurrence of pseudo-steady state flow regime during intermediate flowback periods suggests a "pressure supercharge" effect in the fracture network. Rate and pressure data from this flow regime can be analyzed to estimate key fracture properties (e.g. effective pore-volume and initial average gas saturation in the active fracture network) and drive mechanisms (i.e. fracture closure, gas expansion and water depletion). Fracture closure effects play a significant role in the physics of fluid flow during early flowback periods. However, fluid expansion becomes the dominant drive mechanism towards the end of flowback in gas wells. Flowback data from tight oil wells are dominated by single phase, water depletion during early time periods (about 100 hours). This is unlike many Shale gas wells, which show immediate gas and water production. The concept of dynamic-relative-permeability was proposed to capture the transient, multiphase, fluid saturations in the effective fracture network during flowback. The resulting model enables complementary, 2-phase flowback and post-flowback production data analysis. Qualitative production data analysis show that there is a general correlation between: load recovery and flowback sequence; effective fracture pore volume and flowback sequence; and cumulative water production and effective fracture pore volume. The restriction of comparative load recovery analysis to wells completed in the same formation produces better correlations. Also, this qualitative analysis provides a way to estimate the percentage of the total injected volume left inside and outside the active fracture network respectively. Quantitative production data analysis provides estimates of the pore-volume of active fracture networks, effective half-length and initial gas volume in hydraulic fractures during flowback. This analysis shows that the gas desorption effects from the matrix and the communication interface between secondary fractures and hydraulic fractures, significantly increases as production progresses from flowback to post-flowback periods.

• Subjects / Keywords

  • Analysis Equation
  • Diffusivity Equation
  • Darcy Equation
  • Reactivated natural fracture
  • micro fracture
  • secondary fracture
  • Long term hydrocarbon oil gas forecast
  • Laplace transform
  • Gaver Stefhest algorithm
  • inversion
  • Transient multiphase depletion
  • rapid saturation change
  • Effective pore volume
  • half length
  • load recovery
  • ultimate load recovery
  • Gas desorption effect in matrix
  • Flowback sequence
  • Monte carlo
  • probability density function
  • cumulative distribution function
  • Material balance time
  • Reduction of uncertainty in fracture and reservoir estimate
  • Initial gas
  • oil
  • water volume and saturation in fracture
  • Flowback drive index indices mechanism
  • Dynamic relative permeability
  • Primary fracture
  • hydraulic fracture
  • Model verification with IMEX CMG
  • Water skin
  • block
  • Horn River
  • Anadarko
  • Muskwa
  • Evie
  • Cardium
  • Bakken
  • Matlab
  • Type curve history matching
  • Pore volume differentiation
  • Pressure supercharge
  • Short term period flowback rate and pressure
  • Unconventional tight oil
  • gas
  • sand
  • Shale reservoir Formation
  • Complementary flowback and post-flowback analysis
  • Flowback guided production data analysis
  • Spacing aspect ratio
  • fracture intensity
  • Pay recovery
  • Quadrilinear flow model
  • dual porosity
  • simultaneous triple porosity model
  • Shut in
  • spontaneous and forced imbibition
  • leak off
  • Non linear fit
  • regression
  • generalized reduced gradient
  • evolutionary algorithm
  • Linear
  • bilinear
  • half
  • quarter
  • slope
  • Fate of fracturing fluid left in ineffective fracture
  • Fracture closure
  • compaction drive
  • expansion drive
  • gas drive
  • oil drive
  • hydrocarbon drive
  • Bulk
  • macroscopic
  • permeability and porosity
  • Pseudo steady state
  • unit slope
  • Multi stage horizontal well
  • pad
  • Cross plot
  • flow regime
  • flow region

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3N29PM5M

• 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.