Water flooding and gas coning are potential problems in the horizontal wells drilled to penetrate the oil column in the channel sands of the Hassi R'Mel field. This field is operated by Sonatrach, the Algerian National Oil Company. High Definition Induction Logging (HDIL) in such environments has been used to build a reliable geological model along the wellbore, identify potential problem intervals, and minimize the risk of perforating and producing gas and/or water. The new generation of induction tools - array induction tools - has an advantage of acquiring unfocused data that can be numerically focused to any part of the formation at the post-acquisition stage. Operating at low frequencies with relatively large transmitter-receiver spacings, the wireline array induction measurements can provide reliable information from geological targets up to a 6-m (20 ft) distance from the borehole, depending on resitivity contrasts. In horizontal wells, the induction data may be influenced by adjacent layers located above or below the reservoir. In such cases, when evaluating the water saturation in the near wellbore region, we must, firstly, correct for the influence of the remote layers. Secondly, after correcting the deep HDIL measurements for the presence of the borehole and invasion, we use them to determine both the distance to and the resistivity of remote beds. To integrate the HDIL results into the geological model, a number of issues must be considered. First of all, in the Hassi R'Mel field remote conductive shoulder beds may be either conductive shales or water-bearing horizons. Therefore, to distinguish between the two, their resistivities must differ and, in the interpretation stage, be compared with that of the remote shoulder bed interpretation. In addition, as the measurements do not have a sense of direction, they cannot distinguish between remote beds above or below. Interpretation of the location of an identified remote layer must therefore be based on the geological model for the field as well as other log data. Finally, although an interface between two resistive layers is more difficult to resolve, remote oil-gas contacts may in some cases be found from the interpretation. Presently, every logging job in Hassi R'mel includes an HDIL tool in a string, and the data are usually processed within 48 hours. Providing the geological model and perforating recommendations prior to well completion improves the economics of the well due to increase in oil production and the reduced cost of well recompletion. Introduction More than seventy years after formation resistivity logs were first recorded to identify the presence of hydrocarbons they have lost none of their importance. A particular challenge we face today is to interpret the response of resistivity instruments in deviated and horizontal wells, where formation layering is at a high relative angle or parallel to the wellbore.1,2 Horizontal and highly deviated wells have significantly increased our ability to efficiently produce hydrocarbons from formations where oil recovery otherwise would not be economical. For example, horizontal wells allow us to access the hydrocarbons in thin stratigraphic intervals or where they are sandwiched between an expanding gas cap and an active aquifer. Interpreting the response of today's modern array resistivity tools in these situations is critical to the drilling and formation evaluation process. In horizontal wells, the response of resistivity tools in even a simple layered formation is complicated and may differ significantly from our vertical well-based intuition. However, forward modeling and inversion techniques, from the simplest to the most sophisticated, can assist us with extracting the required information.
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