Extending from Oklahoma into Cooke and Grayson counties in Texas, the Sherman-Marietta basin was formed by the collision and rotation of the North and South American plates. The basin is home to the Ordovician Viola formation, a substantial limestone reservoir with a high degree of vertical fracturing that measures an average of 1,000 feet thick.
This brittle and highly fractured carbonate reservoir poses unique challenges to horizontal drilling. Recently, a privately owned, Ft. Worth-based oil and gas company opted to switch its fluid system in the midst of drilling in order to contend with these difficult conditions. By deciding to partner with Newpark Drilling Fluids (NDF), using its patented, high-performance water-based Evolution® drilling fluid system, the company was able to improve the rate of penetration (ROP) and dramatically increase the planned lateral footage by 1,000 feet as it drilled the well to completion.
The drilling plan called for two wells on each pad. The first well would reach total depth in the Viola limestone at 18,100 feet. The kick off point was at 11,451 feet, with a landing point at 11,888 feet; giving a planned lateral length of 6,212 feet.
In addition to potential trouble posed by the vertical fracturing native to the formation, there were stringers of anhydrite to a depth of 2,800 feet and reactive shale formations with potential for extreme washout all the way to 8,000 feet.
Initially, the operator saw trouble on all trips, with back reaming and pack off issues. Slow ROP while drilling was also an issue. So the decision was made to contact Newpark and displace the incumbent drilling fluid provider. The Evolution fluid system was offered by Newpark in order to improve drilling efficiency. The wellbore depth had reached 5,400 feet at the time of displacement.
Once the Evolution fluid system was circulated two times, drilling resumed. The formula for this well included Newpark’s HiPerm™ shale inhibitor and potassium acetate to maintain wellbore stability through the curve.
The performance of the new drilling fluid system paid off the very next day, when mechanical failures unrelated to the fluid required multiple trips in and out of the hole. But with the Evolution fluid system, tripping out was now much easier. Only one instance of back reaming was necessary and no pack off issues occurred.
The curve was drilled to 45 degrees and a 7-inch intermediate casing was run and cemented on bottom with no issues. The plan for drilling the lateral called for the use of a non-dispersed fluid system as extreme mud losses were expected. Also, Newpark’s EvoLube™ drilling performance enhancer was incorporated into the product mix for improved ROP.
Despite the initial expectation of extreme loss of circulation, no fluid losses were experienced. Torque was between 12,000 and 14,000 foot-pounds through the lateral section. ROP was improved to such a degree that the drilling engineer made the decision to keep drilling until all the drill pipe was utilized, reaching a total depth of 19,100 feet. The final lateral length achieved was 7,212 feet, a full 1,000 feet of additional lateral footage than originally planned, significantly expanding the customer’s exposure to the pay zone in this well.
By making the critical decision to switch drilling fluids in the midst of a troublesome project, this operator was able to realize much higher ROP and sixteen percent more lateral footage than expected. This translated directly into a reduction in drilling days, and improved net present value (from the accelerated completion/production of the well and an increase in the lateral pay zone). This savings provided the operator with a significant return on its investment in NDF’s fluids systems.
In similar cases, operators who partner with NDF and employ the Evolution technology have saved from 10% to 25% on their drilling AFE through enhanced efficiency and reduced time on well, providing a return on investment that has reached as high as 200% to 500%.