This paper describes the evolution in well design and continuous improvement actions during the execution of five shallow and deepwater wells drilled by Repsol using a third generation semi-submersible rig from 2008 until 2010 and the overall improvements from the first well to the end of the campaign.

Sharing this experience will benefit the future construction of post-salt shallow and deepwater wells with oil and gas objectives.

A multidisciplinary team of geologists and drilling engineers started work on these projects in 2007, gathering and analyzing available offset well data from The Santos Basin.

Initially, the quantity of casing and casing point selection followed what had been done in the majority of previous offset wells and the prediction of shallow hazards was performed using the available 3D data.

The knowledge acquired from the top hole sections during the operation of the first well, and more precise pore pressure prediction, allowed us to change the well design for the appraisal well, leaving out a casing point and changing the casing point selection strategy. Later, a more reliable shallow hazard prediction using new 2D high resolution seismic data permitted us to apply the same concept in an exploration well.

As part of the continuous improvement approach followed during well operations the QA/QC procedures were tightened throughout the campaign. The proper use of After Action Reviews at the completion of each well phase was paramount for the lessons learnt from each well and their application to subsequent wells.

Well design optimization and operational performance allowed for a reduction in the number of dry hole days per 1000 m from around 20 to approximately 9.

Good team work between onshore and offshore personnel contributed to a reduction in flat time and an increase in drilling efficiency which contributed to this success story.

The data is of relevance to other oil companies which plan to drill in the Santos Basin and other similar conditions. The achievement of drilling the best well in class, in terms of drilling performance, indicates the success of the planning and execution of the drilling campaign.


The drilling exploration campaign during 2008-2010 in the Santos Basin using a moored semi-submersible drilling rig was the first done in Brazilian waters using a floating rig by Repsol Sinopec Brasil (RSB). The blocks where operations were performed are from ANP round number 7 and the wells are located approximately 180 NM from the shore base. The wells drilled were post-salt prospects in shallow and deepwater at the Santos Basin. The map in Fig. 1 shows the well locations for A, B, C, D and E. In the lower right of this figure is the order that they were drilled together with the water depths.

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