Brian Ellithorp, BlackJack Production Tools
A new gas separation technology was released last year with the goal of creating a substantially increased volume capacity and therefore significantly improved separation quality through application of a process known as limited-entry. This process is more commonly applied to well fracturing and other stimulation procedures wherein the principle is applied to create an equal distribution of fluids to be pumped into an expansive length of producing formation or a variety of formation qualities at once. In the Multi-Stage Limited-Entry (MSLE) separator’s design that same principle is utilized, but in a reversed method such that the fluids being ingested into the gas separator are purposefully restricted through the uppermost chamber and thus the remaining volume must then be handled by the next chamber stacked below. This process continues until the entire volume of fluids designed to be pumped from the well are ingested by the separator stack, at the designed slow pace, and pumped through the rod pump BHA then to surface. The most notable benefit of applying this process to gas separation is that it becomes feasible to slow the intake of the gas-laden fluids by an extreme amount; far more than is possible by simply running a much larger OD poor-boy style separator or a much smaller OD packer-style separator. Slowing down the intake of fluids by dividing the work equally into a stacked set of separation chambers allow for a minimum target of 1.0”/second or less fluid drawdown velocity to become possible which is 6 times slower than other separators are designed for and what their claimed capacities are derived from, yet is what will directly drive far greater ability to reach exceptional levels of gas separation quality and, ultimately, far superior rod pumping production and overall operational success. The MSLE separator manipulates the wellbore and fluid intake path such that the historic and only method of increasing separation capacity, adding more dead-space cross-sectional area, is no longer the primary and also limiting means of improving separation performance. There is only a limited amount of room to work with in historic separation options in the typically applied casing sizes of 7” and, more commonly for the Permian Basin, 5.5”. Getting too aggressive with design applications in effort to add dead-space ultimately leads to either extreme annular superficial gas velocity (resulting in fluid blow-by) when applying a large OD poor-boor style separator with tight tolerance to the casing ID or going the other direction, pressure drop inside the flow-through tube (resulting in potential depositions/plugging) when applying a small OD packer-style separator. This paper will explain the process of limited-entry as it applies to gas separation design and how the resultant MSLE separator functions differ in regards to other commonly applied separators. Further, a notable series of MSLE separator tests will be reviewed to illustrate lessons learned, design improvements implemented, and overall performance achieved in a variety of well conditions.