Abstract

Even the best understood reservoirs are at the mercy of lateral geological heterogeneities which influence production success. To date, horizontal drilling has targeted fractured reservoirs, thin oil plays and reservoirs with known coning problems; some fields are being probed using only horizontal wells. With any of these applications, maintaining the optimum position of the wellbore with respect to productive intervals, while drilling, Is paramount to the success of the horizontal well.

Geological services thus have three key roles to play in the drilling phase of the well. The first role is to find the reservoir through the analysis of marker horizons and real-time correlation with offset data. This permits the directional driller to adjust the penetration angle into the reservoir. The second role is to remain within the reservoir to maximize the wellbore exposure across the productive intervals. The third role is to evaluate the reservoir and advise the reservoir engineer of potential problems prior to completion.

Geological evaluation in horizontal wells has used both mud logging and formation evaluation measurement while drilling (FE-MWD) tools during the drilling phase. In the post-drilling phase, FE-MWD and wireline methods are used to provide logs of the resultant wellbore, together with cores providing key geological insights, when available. Analysis of well data from 6 continents illustrates the many components of successful geological evaluation.

The geologist, as part of a reservoir management team, thus has many geological evaluation tools available both while drilling and after drilling to assist in maximizing the success of the horizontal well.