The Use of “Dope-Free” Tubulars in Petroleum Well Completions

Although invariably well tubulars have been connected with a thread compound to prevent corrosion and the galling of the metal itself, innovative technologies have allowed the introduction of dope-free connectivity by engineering the connections at the end of pipe sections. Avoiding the use of dope compounds has apparent benefits, one of which is the prevention of formation damage. Another is the efficiency and reliability of the operation itself, removing a cumbersome, albeit routine job, a major advantage in the hectic time of a drilling rig’s operation. During the connection assembly a portion of the thread compound is exuded outside the connection and gets access to the well fluids through the tubing and annular space. Laboratory studies by us with core experiments, presented in this paper, show that the dope forms a suspension which penetrates and damages the formation. The damage is severe (more than 99 percent) and will be present in any well injection service. For production the issue is different and will depend on the reservoir permeability and the ability or lack thereof of the dope compound to penetrate the rock matrix or whether it will form a removable filter cake. The reason that this problem has not gained widespread notice is perhaps because the problem has a narrow application of formation permeability, one that we delineate in this work. Additionally, we present evidence that the dope can be washed off usually by simple flow of reservoir fluids and/or brines or it can be partially dissolved by simple solvent treatments employing toluene or xylene. We present here the clear benefits of using dope-free pipe connections by quantifying the negative effects of the alternative. Production equations using a dope-induced skin effect are presented, showing the detrimental impact on well performance.