Enabling Reliable Stimulation of Multiple Perforated Intervals in a Thick Laminated Reservoir: Lessons Learnt in Successful Sequenced Fracturing Evaluation

Abstract

Near-wellbore fracture diversion is a common means of achieving uniform stimulation in long wellbores through heterogeneous reservoirs. A novel sequenced fracturing technique using self-degradable, nondamaging, multimodal particulate pills was deployed for the first time in a clastic rock formation in the Middle East. Application of an advanced design and evaluation workflow to stimulate two perforated intervals in a single continuous pumping operation is presented. Sequenced fracturing with two-step diversion was combined with channel fracturing to increase the chance of successful placement and reduce the inherent risk of screenout. Two proppant ramps were pumped, separated by a diverter pill composed of a multimodal particulate blend and fibers. The size distribution and volume of particles were optimized to create a low-permeability plug in the entry of the primary fracture. The pills were designed so that large particles would intercept the fracture entrance and smaller ones would reduce the permeability of the formed plug, while the fibers would help to maintain the plug integrity both during pumping and once it formed in the near wellbore region. Diversion was confirmed by a pressure increase of 800 psi during the placement of the pill, followed by a new breakdown signature and a treating pressure increase of 500 psi at the same pumping rate. The diversion design was optimized based on the temperature log before fracturing to evaluate the preferential fracture geometry. The evaluation was conducted with a nonradioactive traceable proppant that was pumped in the second proppant ramp to assess the proppant placement using a neutron log. Consequently, a production log was conducted followed by pressure diagnostics. Since the diagnostic results indicated some ambiguity, for a way forward in the field development, the upper interval was refractured and showed high pressures and early treatment termination. The entire flowback timeline was compared, and the productivity index showed no change before and after refracturing. Therefore, multiple pressure diagnostics, post-fracturing flowback enhancement, and the overall intense evaluation verified proppant placement in both perforated intervals using the sequenced fracturing technique. The technique has the potential to save up to 10 days of completion time, which was calculated to yield approximately 40% time and cost savings. This paper presents a complex stimulation treatment analysis that can be utilized to apply the lessons learnt in design and evaluating the success of diversion treatments to aid future treatments. This proven technology enhances efficiency and economics, especially in multistage fracturing, where the efficiency could be enhanced by three- to fivefold.