Method and apparatus for continuous formation sampling and analysis during wellbore drilling

1. Field of the Invention

The invention relates generally to the field of wellbore drilling and formation evaluation. More particularly, the invention relates to devices for extracting samples of subsurface formations during drilling of a wellbore and analyzing such samples with respect to various physical parameters during wellbore drilling.

2. Background Art

Wellbore drilling through subsurface Earth formations is performed, for among other purposes, to provide a hydraulic path from subsurface reservoirs to the Earth\'s surface. During the drilling of such wellbores various instruments are inserted into the wellbore, either during drilling or shortly thereafter, that make measurements of various petrophysical properties of the subsurface formations. Such measurements may include, for example, electrical conductivity, acoustic compressional velocity and shear velocity, neutron slowing down length and related parameters, natural gamma radiation, density, and longitudinal and transverse nuclear magnetic resonance relaxation properties.

The foregoing measurements may be used to estimate the amount of hydrocarbons in place in various subsurface reservoirs, and to estimate the amount of and rate at which hydrocarbons may be produced from such reservoirs. It is known in the art to take samples of subsurface formations for the purpose of making more direct measurements of certain physical properties of the formations, for example, porosity, permeability, and capillary pressure behavior. Such properties are related to the structure of the void spaces of the various formations and are not readily susceptible to determination by the indirect measurements described above without actual formation samples to establish relationships between the foregoing properties and the previously described petrophysical measurements.

One technique for obtaining samples of the subsurface formations is called “coring.” Coring is typically performed using a specialized drill bit, that has an annular drilling surface rather than one that occupies the full cross section of the forward or cutting face of the bit. The annular bit leaves a centrally disposed cylinder of rock formation as it drills the wellbore. In a coring system, the cylinder of rock formation is moved, as drilling progresses, into a non-rotating barrel or sleeve inside a drill string used to rotate the drill bit. Once the barrel is full of core sample, it is typically retrieved from the wellbore. Various core barrels have been devised that may be retrieved without removing the entire wellbore drilling assembly or “string” from the wellbore. Such retrievable barrels can substantially reduce the time needed to obtain core samples, because replacement of the core barrel with an empty one may be performed, for example, by lowering and retrieving an electrical cable or slickline inside the drill string to retrieve the full core barrel and replace it with an empty one so that coring can continue. One such cording system is described, for example, in U.S. Pat. No. 7,124,841 issued to Wada, et al.

As mentioned above, it is known in the art to make petrophysical measurements during the drilling of a wellbore. Instruments used for this purpose are known in the art as “logging while drilling (LWD) instruments. It is known in the art to perform coring concurrently with making LWD measurements. A system and method for performing such functions are described, for example, in U.S. Pat. No. 7,168,508 issued to Goldberg, et al. An advantage purportedly offered by the device shown in the Goldberg, et al., patent is to assure that the depth of rock formation samples obtained by coring is accurately correlated to the depth at which the various LWD measurements are made. It is also possible using such system to select core depths, and to avoid changing drill strings to include core bits where an ordinary “full cross section” bit had been used during LWD operations when the desired core depth is reached.

It is also known in the art to make measurements on the core samples themselves during the drilling thereof. U.S. Pat. No. 5,984,023 issued to Sharma, et al., describes a core drilling system in which the core sample is moved past one or more sensors in order to make petrophysical measurements of the core sample while it is being drilling. The measurements made by the sensor(s) may be stored in a data storage device in the instrument while it is in the wellbore, and/or some of the measurements may be transmitted to the Earth\'s surface using a form of telemetry in which pressure of drilling fluid (“drilling mud”) in the wellbore is modulated, such telemetry being known in the art as “mud pulse telemetry.” Making measurements of petrophysical properties on core samples shortly after they have been drilled and while still at wellbore environmental conditions may provide the advantages of more precise measurements relating to the pore structure and native fluid content of the subsurface formations.

In all of the foregoing coring methods, it is necessary to remove the core barrel after it is filled with core sample. However the core barrel is removed and replaced, e.g., whether by wireline or by removing the drill string from the wellbore, it is necessary to interrupt the drilling process to retrieve and/or replace the core barrel. Such interruption can be time consuming and therefore costly, and particularly in the case of wireline core barrel retrieval, can risk having the drill string become stuck in the wellbore.

There exists a need for a formation sampling and formation sample analysis method and device that does not require interruption of drilling.

A wellbore formation sample acquisition and analysis instrument according to one aspect of the invention includes an annular drill bit configured to couple to one end of a drill string. The bit defines a passageway extending from a cutting face thereof to an exterior surface at a longitudinally spaced apart position from the cutting face. The instrument includes at least one sensor configured to measure a selected parameter of a sample of subsurface formation urged into the passageway by action of the cutting face against subsurface formations. Samples of the subsurface formations are ejected from the exterior surface end of the passageway by the samples entering the cutting face end thereof.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.