Evaluation of Late Cap Rock Failure and Hydrocarbon Trapping Using a Linked Pressure and Stress Simulator
A. E. Lothe, H. Borge, Ø. Sylta, 2005. "Evaluation of Late Cap Rock Failure and Hydrocarbon Trapping Using a Linked Pressure and Stress Simulator", Evaluating Fault and Cap Rock Seals, Peter Boult, John Kaldi
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Hydraulic fracturing and leakage can be controlling factors for hydrocarbon leakage in overpressured sedimentary basins over geological time. Knowledge of the lateral flow properties of major faults is needed to simulate how pressure generation and dissipation can influence the sealing potential of cap rocks. The hydraulic fracture processes in the cap rock need to be evaluated to quantify timing and the amount of hydraulic leakage.
To address these issues, we use a single-phase simulator, which calculates pressure generation resulting from mechanisms, such as shale compaction and drainage, and mechanical and chemical compaction in sandstones. Pressure dissipation and lateral flow are simulated between different pressure and stress compartments defined by major fault patterns at the top reservoir level. An empirical model for the minimum horizontal stress is applied to the Griffith-Coulomb failure criterion and the sliding criterion to estimate hydraulic fracturing.
Only minor changes, if any at all, in the amount and timing of hydraulic fracturing and leakage in the modeled pressure compartments are present when the coefficient of internal friction and frictional sliding are varied. When varying fault permeability, low fault permeabilities give early leakage, whereas high permeabilities result in late or no hydraulic fracturing and leakage. Our simulations also suggest that leakage in one pressure compartment influences the neighboring compartments, and large compartments control the leakage pattern in surrounding areas. The amount of cumulative leakage depends on the timing of leakage and size of the compartment. Uncertainties of timing and leakage for different compartments can be estimated using the pressure measured in the wells today as calibration. The uncertainty in the estimates can be used as guidelines for possible hydrocarbon leakage risks.
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This volume constitutes the proceedings of the AAPG Hedberg conference on seals held in Barossa Valley, South Australia, in 2002. The key driver for both the Hedberg conference and this publication was the recognition that knowledge of risk in the estimation of sealing capacity and fault-seal potential is important in making judgments at the exploration, appraisal, and development stages of the petroleum business. In addition, incorporating seal risk in the overall assessment of hydrocarbons in place can affect decisions to drill prospects and the location of appraisal and development wells, as well as reserve estimation. Improved methods to estimate seal capacity and fault integrity can lead to savings in well costs, improved recoveries through optimum placement of wells, and improved estimates of hydrocarbon in place. This volume contains 18 chapters that reflect the spectrum of presentations at the conference. The knowledge imparted by these chapters will be a window on the state of seal knowledge at this juncture of time and includes topics such as seal failure related to basin-scale processes, the role of geomechanics in seals, and the economic evaluation of prospects with a top seal risk.