US 4,449,594 A · Method for obtaining pressurized core samples from underpressurized reservoirs

Abstract

The invention provides a method for obtaining a balanced, pressurized core sample from an underpressurized geological reservoir formation. A pressure core sampling well is drilled to a preselected depth and the bottom hole reservoir pressure therein is determined. A computer is programmed to compute predicted bottom hole foam pressures at the bottom of the well produced by a stable foam coring fluid, having a preselected composition, which is introduced into the well under preselected control pressures. Measurements are than made of actual bottom hole foam pressures at the bottom of the well produced by the foam when it is introduced into the well at preselected control pressures and under core sample drilling conditions. A comparison is made between the measured bottom hole foam pressures and the computer predicted bottom hole foam pressures to derive a correlation function and to select a correlated core pressure. The selected correlated control pressure produces a foam balance pressure at the bottom of the well which substantially balances the bottom hole reservoir pressure. A core sample is then drilled while said foam is introduced into the well under the correlated control pressure. The core sample is encapsulated while the reservoir pressure within the sample is balanced by the bottom hole foam balance pressure to produce the balanced, pressurized core sample.

Claims10

Dependent claims

A method for obtaining a balanced, pressurized core sample from an underpressurized geological reservoir formation, comprising the steps of:

(a) drilling a pressure core sampling well to a preselected depth;
(b) determining a bottom hole reservoir pressure at the bottom of said well which is to be balanced;
(c) drilling a pressurized core sample while a stable foam coring fluid, having a preselected composition, is introduced into said well at a predetermined empirically correlated control pressure selected to produce a resultant bottom hole foam pressure at the bottom of said well that substantially balances said reservoir pressure;
and
(d) encapsulating said core sample, while said reservoir pressure within said core sample is substantially balanced with said bottom hole foam pressure, to produce said balanced, pressurized core sample.

2 more elements

An apparatus for obtaining a balanced, pressurized core sample from a pressure core sampling well drilled into an under pressurized geological reservoir formation having a reservoir pressure therein, comprising:

(a) foam means for providing a stable foam coring fluid having a preselected composition;
(b) drilling means for drilling a pressurized core sample while said foam is introduced into said well;
(c) encapsulation means for encapsulating said core sample;
and
(d) pressure control means for selecting and maintaining a preselected, correlated control pressure on said foam within said well during core drilling and core encapsulation, said correlated control pressure providing a resultant bottom hole foam pressure at the bottom of said well that substantially balances said reservoir pressure.

2 more elements

Dependencies are inferred from the claim text.

Method for obtaining pressurized core samples from underpressurized reservoirs

Life of this patent

Method for obtaining pressurized core samples from underpressurized reservoirs

Life of this patent

Abstract

Claims10