Advances in drilling and completion technology are resulting in improved recoveries through longer horizontal lateral lengths and larger well stimulation designs. During the early years of the Haynesville Shale development the typical lateral length was 4,500 feet and stimulation designs targeted 1,200 pounds of proppant per lateral foot. Operators in the Haynesville Shale are catching up with the trends prevalent in other basins to drill longer laterals and increase the proppant loading per lateral foot. With today's technology, the typical lateral length has extended to 8,500 feet and in some cases up to 10,000 plus feet with stimulation designs targeting anywhere from 3,000 to 4,000 pounds of proppant per lateral foot.  One of the latest developments in completion tool technology is the dissolvable frac plug. The purpose of this article is to provide general details on dissolvable frac plug technology and the operational and economic benefits when used in longer horizontal laterals.

One of the major obstacles during the completion portion of a horizontal lateral that extends past 8,000 feet is accessing the toe of the lateral with completion tools for the Plug Drill-Out. Even with the advantages of larger OD coil tubing units, extended reach tools such as agitators, and chemicals used to decrease pipe on pipe friction it can be difficult and in some cases impossible to get coiled tubing conveyed tools to a desired depth in longer laterals. Wellbore conditions will have an impact on the difficulty of accessing the toe section of the lateral during drill-out operations. For example, the lateral will have 40-60 frac plugs along with residual proppant from multiple stimulation stages; combine those conditions with the friction points from undesired doglegs in the lateral and the probability of reaching the desired depth to drill-out the toe stage plugs can be diminished greatly.

Dissolvable frac plug technology offers a solution for overcoming the obstacles of reaching deeper, more extended depths in longer lateral wells. Replacing the traditional composite frac plug in the toe section of the lateral with a dissolvable frac plug option eliminates the need to reach the toe section during plug drill-out operations. Dissolvable plugs are made from advanced dissolvable metal and dissolvable rubber material. Dissolvable frac plug technology relies on a combination of three main downhole variables; time, temperature, and/or salinity. There are many different types of dissolvable plugs offered by many different service companies. The dissolution rate for certain plugs may depend more on temperature while others will depend more on salinity. It is important to choose the plug that best fits downhole well conditions. In optimal conditions most plugs will dissolve in 7-10 days.   Upon complete dissolution full wellbore ID is recovered for optimal flow conditions during production and for future operations.  Most dissolvable plugs are limited to 4.5", 5", or 5.5" casing with a differential pressure rating of 10,000 psi. 

Dissolvable frac plugs cost 3-4 times as much as traditional composite frac plugs which potentially equate to several thousand additional dollars associated with plug cost. However, a large portion, and in many cases all of the additional plug cost, will be offset by the reduced amount of lateral that needs to be drilled-out. Decreasing the time of coiled tubing operations associated with running dissolvable plugs will reduce the following costs: coil tubing charges, motor/mill charges, drill-out chemical volumes, fluid volumes, disposal volumes, and all the other associated cost with decreasing the total days of operations. Avoiding extended reach drill outs will also reduce the chances of coiled tubing fishing jobs which can be quite costly and in the worst cases can junk all or a portion of the lateral.