Techbits: Evaluating Test Methods for Exploratory Wells
Authors: JPT staff _ 
Published: February 2015

Well-testing strategies and management approaches to achieve evaluation objectives in the best technical and most economical way generated intense interest among Applied Technology Workshop (ATW) participants in Puerto la Cruz, Venezuela. The 3-day ATW "Testing Exploratory Wells: Rig or Rigless?" prompted a sharing of field experiences and opinions among professionals and industry experts through presentations and discussion, as well as a survey conducted during the workshop.
The technical program comprised six sessions (Exploratory-Well Evaluation Needs, Well-Testing Environment, Perforating and Testing Management, Drillstem Testing (DST) and Rigless Testing Evaluation, Testing-Method Economic Evaluation, and Well-Test Design) including field cases from eastern Venezuela and other locations.
A number of conclusions were drawn from the presentations and survey, including:DST is suggested to test exploration wells.Eighty percent of survey participants use DST.Elements in support of the DST approach are the following:Quality of derived layer evaluation justifies rig time.It supports safety objectives.It has a high degree of uncertainty associated with formation response.Operational contingencies can be implemented quickly.Such a method is imperative in high-pressure/high-temperature wells.
It was also concluded that independent of approach, the use of DST is also dependent on safety, environmental, and expected operational risk conditions while testing. The remaining 20% of survey participants did not disagree on using DST but suggested consideration of rigless testing in case the uncertainties on expected formation testing response are low. Comments included these:Replace DST with permanent-completion testing when dealing with layers of low uncertainty of expected testing response for benefit of savings in rig time and the possibility of an extended test.Layer-evaluation results derived from an integrated study must define an appropriate testing strategy, either DST or permanent-completion testing.In the case of exploratory wells penetrating a zone consisting of known and exploratory layers, DST is suggested for the exploratory layers and permanent-completion testing for the others.Layer-evaluation testing cost associated with DST is higher than that for rigless testing.
From an operational and well-testing data-acquisition point of view, the advantages of DST over rigless testing lie in perforating efficiency, data measurement quality, testing operational flexibility, a reliable downhole shut-in tool, flexible underbalance pressure for perforating, and fluid-characterization quality.
The advantage of rigless testing is that rig time is not a factor to consider when deciding on testing time duration of flowing and buildup periods. It also makes the rig available for other pending jobs.
Present well-testing technology in use by international operators in Venezuela includes both rig-based and rigless technology.
Cochaired by Celia Bejarano of PDVSA and Giovanni Da Prat of Da Prat y Asociados, the Technical Program Committee included Wilton Guevara of Schlumberger; Antonio Carmona, Jorge Daza, Boris Garcia, Victor Garcia, Sergio Inciarte, Luis A. Jimenez, and Miguel A. Salazar, all of PDVSA; Pedro Chira of Halliburton; and Mauricio Moreno of Baker Oil Tools.