Historically all well strings of casing and tubing have used thread compound or “dope” to enable good connectivity, lubricity and sealability of connections. During the makeup of a connection, excess running compound or dope is squeezed out into the annular space where it can gain access to wellbore fluids and cause formation damage. The innovation of surface technologies and industrial coatings allowed the development of dope-free connections. Dope-free technology can potentially eliminate the use of all dopes in well construction.
Formation damage caused by excess pipe dope is not a recently developed problem but has been overlooked in the past. This, perhaps, is because the problem for production applies to higher formation permeability than the ones studied in this paper. For relatively low-permeability formations whose pore throats are smaller compared to dope particles and therefore the latter do not penetrate the rock matrix, the problem can be mitigated by the flow of reservoir fluids The problem can also be diminished by using solvent treatments (such as toluene or xylene) to help break down and dissolve the dope compounds.
The key benefit of dope-free technology is the prevention of damage to the formation caused by dope entering the formation. Additional benefits include a more reliable and robust connection and a more efficient well site assembly process. Dope-free technology guarantees better downhole performance, minimization of galling and other connection damage as well as immediate savings in the operation by removing a routine and uncontrolled manual operation on the rig floor. Reduction of heavy tubular handling and lifting operations as well as the achievement of a virtual no discharge of effluents are also important benefits.
In this paper, we present the laboratory test results utilizing actual core samples. Results show the creation of a harmful dope suspension that can penetrate and damage the formation. During injection operations this can result in severe damage to the well formation (greater than 99%), while in production operations the damage depends on the reservoir permeability. Within the tested permeability range (<288 md), it is observed that the harmful compounds did not penetrate the rock matrix and, instead, it formed a filter cake that can be removed by reservoir fluid flow while in injection mode.
This paper will demonstrate the benefits of using dope-free pipe connections by quantifying the negative effects of the traditional way of joining connections with dope. Various “thread dopes” are tested, showing the differing potential damage from the dope product used. Production equations using a dope-induced skin effect are also presented, showing the detrimental impact on well performance.