Impact of Remaining Water in Hydraulic Fractures on Well Productivity — Field Examples from Saudi Arabian Sandstone Reservoirs

Abstract

The full potential of a well cannot be ascertained if the proppant is not cleaned up properly after a fracture treatment, particularly in tight gas formations. This paper makes an in-depth evaluation of the impact of fracturing water that remains trapped and unproduced within the proppant pack. This water must be differentiated from the condensed water or water from the reservoir that may be produced. The paper studies some of the main fracturing and reservoir characteristics and identifies variables that have a major impact in reducing the proppant pack conductivity and well production. The major variables studied and analyzed are the fracture fluid and broken gel viscosity, the proppant material, closure stress, fracture conductivity, reservoir pressure, and formation permeability. The paper presents an approach to evaluate and correlate different fracture and reservoir variables to the post-fracture sustained production rate. The study was conducted in two steps; first is a sensitivity study using a full scale numerical simulator and using important reservoir properties from a particular gas field in Saudi Arabia along with the characteristics of typical fluids and proppants pumped during a multistage fracturing treatment in horizontal wells in a low permeability sandstone reservoir. The second step consisted of analyzing the actual post-frac water recovery, test gas rate, and long-term production performance. Comparisons are drawn to establish the variables that impact well productivity the most.The paper presents important plots to illustrate the flow back behavior and well productivity under different fracturing fluids scenarios. There have been practical steps taken to minimize fracture damage, thereby maximizing well deliverability. The factor impairing deliverability the most is the unbroken gel viscosity. The early time production behavior is a function of broken gel and fracture conductivity. With the improved treatment scheduling, use of better fluids and proppants, and application of novel completion methods, the well performances have been significantly improved in challenging, heterogeneous, and low permeability reservoirs.

Increased Well Productivity from the Use of Carbon Dioxide to Foam Fracturing Fluids During a Refracturing Treatment in Saudi Arabia

“…It is recommended to flow back the well within 30 minutes to 4 hours before opening the wellhead valves to a small production choke. Historically, the average flowback period in Saudi Arabia is approximately 7 to 21 days from a similar reservoir when using a low polymer zirconium fracturing fluid and even more time when the fracturing fluid is borate based (Rahim et al 2015), although, in many cases, without reaching the necessary low values and decreasing trends in chlorides and basic sediments and water (BSW) percentage. For this case, it took less than one day to reach the cleanup criteria (Fig.…”