A new method is presented for making high resolution, down-hole measurements of porosity and fluid saturations while coring drilling. The method relies on a bank of sensors located in the inner core barrel directly above the drill bit. The sensors allow measurements to be made as the core enters the core barrel and passes by the sensor array. The well-defined cylindrical geometry allows us to construct a cross sectional image of the core at high-resolution (cm scale). The core can then be retrieved to the surface or disaggregated and circulated out as cuttings.

Experimental results are reported for an array of 32 equally spaced electrodes around a cylinder. The electrodes were fired in the opposite protocol, where current is injected across opposite electrodes and measurements of potential differences were made between all other adjacent pairs. The data were then numerically inverted to obtain electrical impedence images (tomograms) of several cross-sections of the core. Results are presented for an oil-saturated 4-inch diameter core from Prudhoe Bay, Alaska. To test the validity of the electrical tomograms, the core was also X-ray CT scanned at high resolution to obtain accurate maps of porosity and oil saturations. A comparison of oil saturations from the electrical tomograms with the CT images shows good agreement.

The possible application of other types of sensors and how they may be used in conjunction with electrical measurements is also discussed. Our results show that it may be possible to make measurements of porosity and fluid saturations down-hole, directly behind the bit, using the proposed method.