On module of E-StimPlan (as seen in the Main Window in the figure) is the option to couple the fracturing simulation (the “frac”) with a wellbore, gravel pack simulation (the “Pack”). This module, its appropriate use, and brief user instructions are included below. NOTE that the appropriate “gridded model” (E-StimPlan or fully 3D) MUST be selected in order to utilize the “Frac-Pack” module.
For most frac-pack completions, it is NOT necessary to use the “Frac-Pack” simulation. That is, for the “frac” part of a Frac-Pack (i.e., either the design, and/or analysis of the frac), simulating the “Pack” (i.e., the wellbore, gravel pack part of the operation) is NOT required. When then should this capability be utilized?
Typical cases that might warrant a wellbore simulation might include:
As a final note — NOTE that the Frac-Pack simulation is not really intended to give any specific output as to the wellbore pack. It is intended to examine “problem cases”, and to use that examination as an aid in determining the “cure”.Case History
The user notes below are based on a relatively shallow Gulf of Mexico frac-pack case history. This is briefly illustrated in the figure below. The geology is relatively simple, a simple shale, oil sand, shale environment. Pre-frac tests shows closure pressure equal to 3560 psi, and bottomhole treating pressure throughout the gel mini-frac injection was above 3780 psi. For the subsequent main fracture treatment, from a time of 461 to 475 minutes, the injection pressure is essentially identical to the pressure during the gel mini-frac. Then, at about 475 minutes, the bottomhole pressure begins to increase possibly indicating the start of the desired tip screenout (TSO). However, at about 478 minutes, bottomhole pressure begins to drop. It drops below the 3780 psi injection pressure seen during the mini-frac, and later drops below the closure pressure of 3560 psi measured earlier.
How is this possible? This definitely qualifies as “unusual” behavior that needs to be understood prior to future fracs. In addition, while sand control was achieved, post-frac production was very dis-Frac-Pack Simulation Option Page 2 of 9 appointing with a well test showing a positive skin of +32! This is one type of case where the “FracPack” module must definitely be utilized for post-frac analysis.
User Notes – Input
To run a “Frac-Pack” simulation, first “Frac-Pack must be selected (along with the gridded model appropriate for the expected fracture geometry) from the StimPlan Main Window (as seen above).Simulator Data
If “Simulator Data” is then selected, the “Frac-Pack” input tab (upper-left) will be active, and this special input dialog can be accessed. This will require a completion diagram as seen in the figure below. This well completion information can be used to input the required depths, diameters, etc. needed for the wellbore simulation.
The data below is found by opening the StimPlan file: Tutorial_Frac_Pack_01.STP.
In addition, input must be provided for:
Friction data input is the same as for normal fracturing cases, and this input dialog is identical to the input found under the “Frac Data” tab at the top-left. Note, however, that the inputs for the pipe friction data is NOT for the gravel pack screen/ liner annulus, etc. The pressure drop inside the gravel pack area is calculated internally within the simulations. The pipe friction input data is strictly for the tubing from surface to the top of the crossover.
However, some input for perforation friction is REQUIRED for the Frac-Pack simulations.User Notes – Execute
The simulation for a “Frac-Pack” model is the same as for any fracture case. Simply select “Run Frac Simulator” from the StimPlan main window. When the simulation is completed, the Graph Menu will be displayed as seen in the figure. The “Frac-Pack” output will now be active, as seen circled in red.
The only special output for “Frac-Pack” simulations is via the special plots opened using the “Frac-Pack” graph selection above. This opens the graph module seen in the figure, and this includes four output options.
This discussion has illustrated a typical utilization of the “Frac-Pack” module. The case in question showed very poor well performance, and unexpected bottomhole pressure behavior. The question was “What caused these two things, were they connected, and what can be changed to “cure” the problem?”.
The “cure” appears to be to control the massive height growth into the shale. As seen below, if one selects the “Reduced Perforation Interval”, and then re-runs the Frac-Pack Simulation, the results are drastically different. Massive height growth into the shale is avoided, with a resulting very good fracture, a large net pressure increase, and a good wellbore pack over the target formation.