Tool Weight analysis – an Engineering Approach to Optimize Pressure Temperature and Spinner Data Acquisition

Abstract

Pressure Temperature Spinner survey (PTS) is one of the key logging tools that is very important for reservoir characterization and surveillance. PTS data are useful for prediction of reservoir productivity zones and their contributions.This too requires ideal conditions during the survey, meaning that the condition during the logging survey should be similar or as close as possible with the normal well operating condition particularly the production rate. Operating the well during the survey at high flow rates to enable reliable data acquisition and accurate interpretation is not as easy as it appears. Logging the well particularly at such conditions always come with the risk of losing the tool in the wellbore from excessive “bumping” due to flow turbulence, or in rare cases, tool and cable being cut and going up out the wellbore into the production lines. Consequences of the presence of fish and cable in the wellbore or production line will potentially impact profitability. For example, the PTS tool cost about $ 100,000-150,000. and cost of fishing tool and cable cost a minimum of $20,000. Data acquisition alone costs about $ 10,000 and excessive “bumping” of the tool degrades the quality from the spinner. Estimating the proper weight of the tool given the conditions in a well is traditionally done by trial and error. An initial estimate of the flow parameters (usually with the assumption of a homogeneous fluid) in the production casing (above the production liner) is used to calculate the required tool weight. The tool is then run in the well and if “bumping” occurs as observed in the cable tension, the well production rate is then reduced. If the production rate during the test is deemed too low, the tool is then pulled out of the hole for weight to be added to the tool assembly or the configuration changed. This poses significant risk and delays to the survey. The actual fluid flow characteristics, particularly for 2 phase wells, are quite complex even in the production casing with brine flashing to steam. Inside the production liner (within the reservoir) multiple fluid entries with varying fluid enthalpies compounded by varying wellbore diameters (as in the case of telescoping wells) further increases this complexity Tool Weight Analysis (TWA) is an engineering approach that integrates modeling of the fluid flow in the well and its impact on the logging tool and cable. It is basically a calculation of forces between the tool/cable components and flowing wellbore fluid.