Look ahead pore pressure prediction

Abstract

A method for predicting jumps in pore pressure of a subsurface includes the steps of obtaining a porosity and a resistivity log value while drilling; dividing a cross plot of the porosity and the resistivity log values into two regions where the split of the two regions is based on the following (I): R=0.062 / ø1.5; averaging the obtained porosity and resistivity log values in the subsurface within a set interval to obtain a representative value of resistivity and porosity for the subsurface within the set interval; and giving a first warning of a high overpressure region if the representative value of resistivity at the representative value of porosity is lower than 0.062 / ø1.5. The method may also include giving a second warning that a jump in pore pressure is coming within 100-300 meters if the normalized values of resistivity and porosity has a turning down point in its trajectory.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to look ahead pore pressure prediction. This system provides a warning if a high overpressure regions is being drilled. The system then provides a second warning when a high overpressure sand is approaching within 300 meters from the drill bit.[0003]2. Description of Background Art[0004]FIG. 1 shows an exemplary diagram of a drilling operation. One of ordinary skill in the art will appreciate that the drilling operation shown in FIG. 1 is provided for exemplary purposes only and accordingly should not be construed as limiting the scope of the present invention. For example, the drilling operation shown in FIG. 1 is a seafloor drilling operation, but the drilling operation may alternatively be a land drilling operation.[0005]As shown in FIG. 1, a drilling rig 105 is configured to drill into a formation (e.g., a formation below a seafloor 110) using a drill bit (not shown) coupled to the dist...

AI Technical Summary

Benefits of technology

The present invention provides a method for predicting jumps in pore pressure of a subsurface by analyzing logs value while drilling. The method involves obtaining at least two logs value (e.g., density and resistivity) or a combination of multiple variables (e.g., density, shear velocity, and resistivity) from the shale formation. These logs are then normalized by removing the effect of salinity and other factors that may affect the measurements. The normalized values are then used to create a cross plot of resistivity and porosity, which is used to identify high overpressure regions. The method also includes detecting upcoming sudden pressure increases and presetting a pore pressure jump in the deepest section of the formation. The use of multiple variables in a multivariate manner improves resolution and accuracy.

Problems solved by technology

The presence of hydrocarbon in that section could compromise the resistivity measurement within the neighbor shale.

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