The MEL* Mechanical Efficiency Log is a realtime interpretation technique to evaluate bit efficiency, tooth flatness and in-situ strength of the formation. The method is intended to be used in formations which behave plastically and are drilled by a gouging or scraping action of the bit. Suitable drilling combinations include series 1 and series 2 bits in shale, claystone, or silt formations.
Bit efficiency is traditionally evaluated by analyzing surface measurements of weight on bit and torque. The measurements provide ambiguous answers due to the influence of the drill string interaction with the wellbore. MEL solves the problem with use of downhole measurements which are not affected by frictional losses along the drill-string. Downhole weight on bit (DWOB*) combined with downhole torque (DTOR*) determines the amount of energy expended at the bit. This energy is analyzed to separate bit effects from formation effects.
Surface parameter data is stored within the IDEAL system to be analyzed with the associated downhole measurements. The surface parameters include rate of penetration, hook load, surface torque, and revolutions per minute. Comparing surface measurements to downhole measurements provides the con stant monitoring of bit wear. Drilling efficiency can be directly related to bit and formation conditions which allow the most efficient use of bit life.
Downhole and surface data are presented for interpretation in the form of tables, logs, and crossplots. Key outputs calculated by MEL include the following:
By simultaneously comparing the individual outputs, the proper decision can be made concerning when and when not to make bit trips. Reducing the number of trips increases the amount of productive time spent rotating the bit.
Measuring bit efficiency and formation strength in real time identifies bit problems before they lead to a fishing event.
Accurate real-time correlation with offset wells uses historical depth-based drilling data to reduce drilling problems in the current well.
The Correlation Screen provides a tool to locate the position of various formation markers and targets while drilling. A graphical display of current log information positioned next to offset logs provides real-time correlation to determine bit position in the current wellbore.
Formation identification is often difficult due to unpredictable formation pinch-out, dip, faults, etc. The Correlation Screen provides the option to select up to three logs from an offset well for comparing with realtime data from the current well. Once corresponding behavior between logs is observed, correlation points are selected which automatically depth-shift the logs. The graphical comparison helps determine bit position relative to anticipated formation layers. Previous knowledge of formation layers provides the driller with necessary preparation time to circumvent potential hole problems.
The IDEAL system contains several methods to import data from offset wells. The most efficient method is through previously recorded well data from the IDEAL system itself. The survey file can also be obtained from a PowerPlan survey file. An import option converts a PowerPlan or any ASCII file with columns of data containing measured depth, inclination and azimuth to the proper format.
The customizable correlation screen is capable of comparing offset well curves with the current well information. Up to three curves from each well are presented against a given depth reference. The reference may be one of true vertical depth (TVD), true stratigraphic thickness (TST), or true vertical thickness (TVT). An array of log information may be displayed including gamma ray, density, neutron, and resistivity data. Once the data channels are selected, the depth reference can be switched between TVD, TST, and TVT.
The correlation screen plots the offset well data alongside current well data as it is being drilled. Scroll bars on each log provide a means to shift well plots individually. With the logs presented side-by-side, correlation points care selected on the offset and current well that represent the same geological boundary. The user is able to make multiple correlations which will cause offset well logs to be appropriately stretched or compressed as a result of the shifting depths. The offset well data will always be labeled with the correct depths regardless of the shift applied. The resulting screen plot provides a reference to inform the driller of the bit location relative to potential hole problems.
Was this article helpful?