Pushing the Envelope for Production Logging in Extended Reach Horizontal Wells in Chayvo Field, Sakhalin, Russia-New Conveyance and Flow Profiling Approach

Abstract

Production logging and flow profile interpretations are necessary to properly assess completion performance and interpret pressure buildup data in Chayvo Field. With a lateral reach in excess of 8 km, acquiring production logging data is difficult. Memory logging, with conventional production logging tools via coiled tubing and a hydraulic tractor, was employed. However, due to the wear experienced by the coil, high cost, and poor data quality at low flow rates, this technique was abandoned after initial logging efforts. Development of a state-of-the-art electrically powered tractor, combined with new surface read out array mini-spinners and optical gas and array resistivity water holdup sensors, provided a viable logging alternative with a 40,000 ft cable specifically manufactured to avoid splice induced weakness. This new logging technology detects and measures stratified flow and lower flow rate fluid entry than conventional axial symmetric production logging tools in ERD well bores. The equipment has recorded production logs to a measured depth of 9,775 m at a true vertical depth of 2,613 m. Comparison of cumulative flow rates from the array mini-spinner analysis to the logging-while-drilling derived cumulative permeability-thickness product has enabled the evaluation of the completion methodology. Based on the production log analysis, the new completion methodology appears to have restricted flow from the higher permeability intervals while permitting flow from lower permeability intervals. The methods used to plan and execute these production logging programs, and the integration of the interpretations into the pressure-transient analysis for the complex completions of multi-layered reservoirs, are discussed. Examples illustrating data quality and interpretation are provided. Introduction Chayvo wells have long sail sections at angles greater than 70° over several kilometers followed by a horizontal section of 1–3 kilometers extent. These wells intersect multiple reservoirs at low dip angle that are produced with a single commingled completion and well test interpretation requires accurate estimation of the relative flow rates from each producing reservoir. Conventional wireline logging is not possible because of the high-hole angle and the long reach. Wireline logging using typical tractors is not practical either because they do not provide enough tractive force to reach the toe of the well. Conventional coiled tubing conveyed logging was also not practical because of the friction produced in the long-reach wells. This left two possibilities: coiled tubing conveyance with a hydraulically powered tractor or wireline logging with a new much more powerful tractor. Examples using both types of conveyance are given here. Production log interpretation in horizontal wells is complicated, particularly with two-phase (gas-oil) flow down-hole as in Chayvo. Interpretation with a conventional turbine spinner or a full-bore spinner becomes inaccurate in these cases, causing reliance on the temperature log which is also difficult to interpret since the geothermal gradient is essentially zero in a horizontal well. Interpretation gets more difficult once water breakthrough occurs. Array holdup tools of capacitance, optical, and resistance type have been available for some time [2,4]. Recently, an array mini-spinner has been introduced that has proven quite useful in better characterizing stratified flow in high-angle wells [5]. General Well Description The main oil productive reservoirs in Chayvo lie 8–9 km offshore from the drilling rig location at depths of 2400–2900 m TVDSS (see Figure 1). Reaching these reservoirs requires a short vertical shallow section building to a sail angle of 70–75° to reach the landing depth of the 12–1/4″ hole that is in the shale that seals the primary reservoir. The well is then drilled horizontally into the primary and secondary reservoirs at a depth that is approximately midway between the GOC and OWC.