We present perforating on wireline with dynamic underbalance (DUB) to simultaneously maximize productivity and minimize gunshock. We focus on perforating on wireline with DUB because, when compared with other approaches, perforating with DUB is probably the best method to deliver lower tunnel plugging and lower formation rock damage, with lower risk of tool damage due to gunshock or guns blown uphole. Specifically, we present two important aspects of perforating on wireline using DUB: prediction of wellbore dynamics to assess perforation tunnel and formation cleanup and gunshock prediction to assess the risk of tool damage. We present the latest models used to evaluate perforating jobs for well productivity and for operational risks.
It is well known that the DUB produced when perforating with the right gun system can remove formation rock damage and tunnel plugging produced by shape charges. What is not so well known is how much DUB (amplitude and duration) is necessary, and how to predict how much DUB will be generated by a gun system. To achieve formation tunnel cleanup, we need a DUB of large amplitude but short duration to remove perforating rock damage and plugging while minimizing gunshock loads. In the pre-job design, we simulate/predict the transient fluid pressure waves in the wellbore and formation rock to predict formation rock damage cleanup and also the associated gunshock loads. DUB amplitude and duration depend on job parameters that can be adjusted, such as type and size of guns, loading of standard perforating charges and DUB charges, and placement of packers, if present. Important physics included in the model are: gun filling, wellbore pressure waves, transient reservoir fluid flow, and the dynamics of all relevant solid components (cable, shock absorbers, tools, and guns).
The reliability of the DUB prediction model is demonstrated by comparing downhole fast-gauge pressure data with the corresponding simulated values. When the reservoir properties are well known, the predicted DUB amplitude and duration are very close to the field data values, typically within 15% or less. The reliability of the gunshock loads is demonstrated with residual shock absorber deformation and cable tension logs. We also demonstrate how gunshock simulations have been useful to explain equipment failures due to gunshock loads.
Reliable predictions of wellbore dynamics, transient reservoir flow, and gunshock loads enable operators to select perforating equipment capable of removing perforating formation damage and reduce the risk of unexpected release of tools and guns due to dynamic loads, thereby minimizing the probability of nonproductive time and fishing operations.