Print this pageDrilling Environment Created Data Issues Resolved Through Innovative Data Gathering and Interpretation Techniques
Directional drilling processes that involve down hole motors, diamond bits and bent subs have substantially changed the dynamics and economics of drilling to smaller and more specific geologic targets. This process produces some drilling induced artifacts including grooves and bit chatter in the well bore wall. These created environments radically affect the performance of many of the accepted logging tools used in the industry. This alters the log responses and distorts the needed answers. This sometimes leads to erroneous completion decisions.
Standard wireline density logs, since they require good pad to formation contact, generally produce error prone porosity values in rugose boreholes. The porosity cycles high and low as the pad loses, then regains contact with the formation. The neutron porosity is also affected in many cases, exhibiting an identical cyclical character. The porosity measured by either traditional log is at best suspect and at worst incorrect and also effects crossplot porosity estimation. Another method such as mandrel deployed NMR logging can be used to get valid porosity data. Pad deployed NMR devices are also affected in rugose wellbores.
Dipmeter analysis can also be affected as drilling induced artifacts can be misinterpreted as geologic events. The drilling induced grooves provide very distinct electrical contrasts and the analyst may interpret the grooves as actual geologic features. Another complicating factor contribution to the dipmeter interpretation challenge was the use of an oil base mud system. Oil base dipmeter interpretation was not consistent with expected results.
To solve both of these difficult interpretation challenges requires a different set of logs that provide answers independent of borehole quality. In this paper, we show how centralized mandrel deployed NMR logs, unaffected by bore hole irregularities, were used to define effective porosity. We also show how oil base imagers were used to differentiate between drilling induced grooves and beds or formation boundaries. This paper will discuss some examples wherein we showcase log interpretation techniques that were used to overcome the operational issues of oil based mud environments and to define actual geologic events.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil