The 3D Explorer Induction tool delivers a more accurate evaluation of laminated sand-shale sequences and was developed to provide improved identification and quantification of hydrocarbons.

Conventional resistivity tools often miss hydrocarbon pay zones in thinly laminated sand-shale sequences. Conventional tools measure horizontal (bed-parallel) resistivity, and the measurements are dominated by the low resistivity shale laminae, not by the high resistivity hydrocarbon-bearing sand laminae. In many horizons, these formations produce at economic rates and contain significant reserves. The unique 3D Explorer Induction tool enables determination of both bed parallel (R HORIZONTAL ) and bed-normal (R VERTICAL ) resistivities and is designed to be run in standard combination with the HDIL instrument.

3D Explorer Induction responses highlight laminated sand-shale sequences with potential hydrocarbon productivity. When petrophysical analysis of the interval includes 3DEX data, hydrocarbon volumes are increased, when compared with analysis using conventional resistivity data. Results also indicate a much better agreement with capillary pressure curves derived from core analysis.

The 3D Explorer Induction Logging Service (3DEX) employs sets of Z direction coils coaxial with the instrument and additional orthogonally mounted X and Y coil arrays. Inversion processing of 3D Explorer Induction data allows computation of horizontal and vertical resistivity, enabling determination of the resistivity transverse anisotropy. Conventional logging tools generate currents parallel to the formation bedding layers in boreholes that are drilled perpendicular to the formation. In this situation, instruments such as the High-Definition Induction Log (HDIL) measure the horizontal conductivity. In thinly laminated or thinly bedded reservoirs, the horizontal conductivity is governed by the conductive shaly laminae of the formation. For example, in a hydrocarbon bearing sand-shale sequence, the shale resistivities could measure 1 ohm-m. Within the sequence, hydrocarbon bearing sand layers could measure 10 ohm-m, with a net-to-gross of 50 percent. A resultant horizontal resistivity measurement of 1.8 ohm-m would be observed. The low shale resistivity is the dominant part of the measurement, obscuring the presence of the hydrocarbons. The vertical conductivity measurement is very sensitive to the presence of the hydrocarbon filled sand layers and would increases to about 6 ohm-m in the example described above. The physical phenomenon is resistivity transverse anisotropy.

• Determine accurate Sw in thinly bedded sand shale sequences
• Determine resistivity anisotropy

• More accurate formation resistivity, water saturation, and reserves estimates in thinly laminated or other non-uniform reservoirs
• Better resistivity estimates in highly deviated wells