30 Years of Horizontal Production Logging. What are We Really Measuring?

Abstract The objective of this work is to demonstrate that the choice of the conveyance method for Production Logging operations is key in horizontal wells, as it affects the flow dynamics and changes the well inflow performance compared to undisturbed flowing conditions. A case study is presented, showing that critical decisions to develop a field (or not) may have been wrongly influenced by Production Logging results, if the effects of the conveyance on the inflow distribution were not correctly understood. Synthetic production logs and flowing pressure distributions along the horizontal section were computed, and sensitivities on conveyance method diameter (coiled tubing, tractor and cable), pipe diameter, well length and reservoir properties were also conducted. These results were compared with the normal well flowing conditions to establish the representativeness of the PL measurements. A method for simulating the undisturbed production profile is presented, which uses the results of a Multirate Production Logging and recomputed flowing pressures using nodal analysis. The presence of the conveyance method alters the well's inflow performance and zonal contributions, due to the modifications of the flow geometry and additional frictional pressure drop. The bottomhole flowing pressure is disturbed, with lower pressures around the heel and higher towards the toe. The drawdown along the horizontal gets modified, acting as a preferential choke for production coming from the toe and increasing the driving force for production from the heel. The severity of the drawdown unbalance is a function of the induced frictional pressure, given by the pipe and conveyance diameter, well length, flow rates, etc. The simulations and sensitivities presented in this paper help to understand how significant the PL measurements are, and when these results become misleading. The case study supports these findings, where the pressure disturbance induced by the conveyance changed the flow distribution dramatically, wrongly indicating than an area of the field was relatively depleted compared to the zone around the heel. The lack of understanding of the impact of the conveyance method can lead to poor developmental decisions.