oa A Consistent Geostatistical Approach for Constraining Multiple Surfaces to Horizontal Wells

The robust use of horizontal well data in 3D stratigraphic horizon modeling is an important challenge.<br>In many reservoir models there are inconsistencies between the zone log information observed in<br>horizontal wells, and the horizons and zones of the 3D model.<br>The two main reasons for these inconsistencies are that:<br>1) Zone log information is not used directly in the modeling of the surfaces;<br>2) Well picks in deviated wells do not impact the modeling of adjacent surfaces.<br>Inconsistencies between the 3D model and the horizontal well data are typically resolved by time<br>consuming, iterative manual editing of the stratigraphic horizons.<br>A robust, geostatistical approach for ensuring the correct modelling of multiple stacked stratigraphic<br>surfaces constrained by long horizontal wells is presented. The approach has been developed to<br>maintain 3D consistency between the stratigraphic surfaces and horizontal well data. The stratigraphic<br>surfaces are treated simultaneously in 3D and universal or Bayesian cokriging is used for prediction of<br>surface location based on a variety of constraints including: well picks; zone logs; isochores and<br>seismic interval velocities.<br>In contrast to standard approaches, all well markers (picks) are treated simultaneously and will have<br>impact on surfaces above and below. This ensures consistent use of all available well marker data forall surfaces.<br>Zone log constraints in long horizontal wells are handled by identifying the sections of the well paths<br>that impose soft (inequality) constraints on the surfaces. The key sections of the horizontal wells are re<br>-sampled at approximate grid resolution and used as help points in the kriging equations. Identifying<br>the soft constrains and assigning correct value to the help points is the cornerstone of the method.<br>Velocity and isochore trends are used to ensure that overall shape of the structure and thickness<br>variations are preserved. Uncertainty trends for velocities and isochores are used to allow flexibility in<br>the relative weights assigned to the various input constraints.