Pressure Safety System for Use With a Dynamic Annular Pressure Control System

Abstract

A method for controlling formation pressure during the drilling of a borehole through a subterranean formation includes selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole. The drilling fluid is discharged to a reservoir to clean the drilling fluid for reuse. Annular space fluid pressure is selectively increased to maintain a selected fluid pressure proximate the bottom of the borehole by applying fluid pressure to the annular space. The selective increasing includes controlling an aperture of an orifice operatively coupled between the annular space and the reservoir. Fluid from the annular space is discharged other than through the orifice when the annular space fluid pressure exceeds a selected value, or drops below a selected value.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]Priority is claimed from U.S. Provisional Application No. 60 / 793,488 filed on Apr. 20, 2006.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not applicable.BACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]The invention relates generally to the field of drilling boreholes using dynamic annular pressure control devices. More specifically, the invention relates to method for determining borehole fluid control events, such as loss of drilling fluid or formation fluid entry into a borehole when such devices are used.[0005]2. Background Art[0006]The exploration for and production of hydrocarbons from subsurface Earth formations ultimately requires a method to reach and extract the hydrocarbons from the formations. The reaching and extracting are typically performed by drilling a borehole from the Earth's surface to the hydrocarbon-bearing Earth formations using a drilling rig. In its simplest form, a land-base...

AI Technical Summary

Benefits of technology

[0018]One aspect of the invention is a method for controlling formation pressure during the drilling of a borehole through a subterranean formation. A method according to this aspect includes selectively pumping a drilling fluid through a drill string extended into a borehole, out a drill bit at the bottom end of the drill string, and into an annular space between drill string and the borehole. The drilling fluid is discharged to a reservoir to clean the drilling fluid for reus...

Problems solved by technology

The fact that the drilling fluid hydrostatic pressure typically exceeds the formation fluid pressure also results in the fluid entering into the formation pores, or “invading” the formation.

Overbalanced drilling relies primarily on the hydrostatic pressure generated by the column of drilling fluid in the annular space (“annulus”) to restrain entry of formation fluids into the borehole.

However, the addition of density increasing (“weighting”) additives to the drilling fluid: (a) may not be rapid enough to deal with the formation fluid influx; and (b) may cause the hydrostatic pressure in the annulus to exceed the formation fracture pressure, resulting in the creation of fissures or fractures in the formation.

Creation of fractures or fissures in the formation typically results in drilling fluid loss to the formation, possibly adversely affecting near-borehole permeability of hydrocarbon-bearing formations.

The use of overbalanced drilling also affects the depths at which casing must be set during drilling operations.

Borehole fluid pressures in excess of the formation fracture pressure can result in the drilling fluid pressurizing the formation walls to the extent that small cracks or fractures will open in the borehole wall.

Further, the drilling fluid pressure overcomes the formation pressure and causes significant fluid invasion.

Fluid invasion can result in, among other problems. reduced permeability, adversely affecting formation production.

As noted above, while additional weighting material may be added to the drilling fluid to increase its hydrostatic pressure, such will be generally ineffective in dealing with a gas kick due to the time required to increase the fluid density at the kick depth in the borehole.

An open loop drilling fluid system is subject to a number of other problems.

It will be appreciated that these pressure spikes can cause fatigue on the mud cake and borehole wall, and could result in formation fluids entering the borehole or fracturing the formation again leading to a well control event.

It has been a concern in the industry that the use of DAPC systems such as disclosed in the van Riet '981 patent that plugging of any part of the backpressure system such that discharge of the drilling fluid from the annulus back to the mud tank or pits is restricted may result in damage to the borehole.

Another concern expressed in the industry is that failure of the backpressure regulating components to hold the backpressure may result in loss of pressure control over the borehole.

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