Data Mining of In-Situ Stress Database Towards Development of Regional and Global Stress Trends and Pore Pressure Relationships

Abstract

The in-situ stress, and in particular the minimum principal stress, is a major controlling parameter for many subsurface engineering issues, such as safe injection and injection pressure limitation, wellbore stability, fractured injection and stimulation, and completions optimization. In addition to these more ‘traditional’ field development decisions, in-situ stress has direct influence on the rapidly growing CCS industry, where storage volumes of CO2 are highly dependent on the initial minimum effective stress margins available in the sealing caprock(among other factors). In this work we investigate a unique in-house stress database, obtained through decades of dedicated stress testing, to better understand and quantify the relationship of in-situ stress versus depth and its relation to pore pressure. Focus is primarily on the Norwegian Continental Shelf but global results from additional passive continental margin areas are also incorporated and compared. We find that, almost regardless of the geographic area, when hydrostatic pore pressure conditionsapply, relatively simple linear relationships exist of stress versus depth and that the assumption of normally-stressed/relaxed stress regimes can be applied with a good degree of certainty. Further, where overpressure conditions are present, relationships dependent on the degree of overpressure are defined, both regionally and globally. The resulting overpressure relationship is found todiffer fromthose commonlyaccepted andused throughout industry, e.g. Breckels and van Eekelen 1982. Finally, the resulting stress trends versus depth are investigated to better identify the potential presence of high stress environments such as deeper strike-slip to reverse faulting regimes that can complicate field development decisions. While of interest to the hydrocarbon industry in general, the results of this work are highly valuable to under-explored areas where in-situ stress data is not yet available, e.g. saline aquifer prospects targeted for eventual CCS development.

Reducing Uncertainty in Site-specific Stress Prediction for CO2 Storage in the North Sea, Norway

“…Of the publicly available NPD stress database, Figure 1a shows the distribution of 𝜎 h versus depth (< 3,000 m) for each site within the study area containing Aurora and Smeaheia, and reveals a certain degree of similarity between the stress trends at the 11 sites. Such similarity, aligned with other published results [2], may be attributed to the relaxed sedimentary basins where gravitational loading dominates the lateral stress distribution rather than tectonic components, with the between-site variation arising from differences in the geological conditions and pore pressures [3]. When facing limited data for a site like Aurora and Smeaheia, the current approach is often to either directly use the stress trend from other sites having richer data or expand the coverage area to include more data.…”

“…where no data is available, the standard approach is to perform a classical linear regression on stress data versus depth and treat the fitted trend line as the best site-specific stress predictions along depth [2]. However, stress data are often highly limited at CO2 storage sites; for example, Aurora and Smeaheia have only five in situ stress measurements available at best respectively.…”

Importance of Drilling-Related Processes on the Origin of Borehole Breakouts - Insights from Lwd Observations

“…52 All formations within the sedimentary sequence are situated in a normal faulting environment, close to isotropic stresses. 53 The stress regime in the basement is assumed to be unrelated to that in the sedimentary sequence. 54 References to the geology and the geomechanics of the hydrocarbon fields are provided in Table 1.…”