In this paper we describe a perforating technology that helped deliver highly productive wells in the Tunu field, a multilayer sandstone gas reservoir in Indonesia. We describe the simulation models used to evaluate perforating designs and operational risks, and we include post-job productivity data for 9 wells, all of which ended up delivering more than 500% of the expected productivity, in large part due to highly conductive perforation tunnels. The intervention technique used in the Tunu field is based on applying Dynamic Underbalance (DUB) perforating with a nitrogen kick-off technique to perforate on balance or slightly under-balance. This technique enables perforating long intervals with deep penetrating charges at high shot density, and with very low risk of gun jumping. This technique also promotes natural well flow after perforating, without the extra cost of coiled tubing intervention to perform liquid unloading. We discuss several aspects of job design and simulation. Predictive simulations based on API RP 19B Section 4 data and rock perforating models for sandstones indicated that perforating damage clean-up with dynamic underbalance would deliver the highest well productivity. The simulation model that predicts wellbore dynamics, namely pressure waves in the wellbore, at the sand face and inside the reservoir, also predicts the gunstring dynamics with the associated gunshock loads on the conveyance. Gunshock simulations showed that the DUB technique also minimizes operational risks. All the important aspects of the DUB perforating technique were predicted in the job planning stages. Guns were custom loaded to produce a good dynamic underbalance to remove the low permeability crushed rock zone from inside and around the perforation tunnels, thus minimizing perforation skin and maximizing well productivity. In many cases well productivity turned out to be exceedingly high, more than 500% of the initially expected productivity for7 DUB perforating jobs and 2 DUB post-perforating clean-up jobs.

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.