Propped Fracturing as a Tool for Sand Control and Reservoir Management

Abstract

Summary Hydraulic fracturing has historically been a prime engineering tool for improving well producing rates, either by circumventing near-well damage or by stimulating well performance. This paper describes a somewhat new fracturing application where increasing rate was not the primary goal. In this case, the goal for fracturing was modification of the flow profile to allow a more uniform vertical production profile and thereby maximize sand-free rates over the perforated section of the reservoir. In best cases for such applications, this technique allows perforating of "weak" rock to be skipped, reduces risks of sand production, and allows greater wellbore drawdown through perforated intervals in more competent reservoir rock. This allows better long-term productivity and improved recovery and total project economics. In short, it was hoped that propped fractures would improve reservoir management of the Etive/ Rannoch formations in the Gullfaks field. Introduction The Gullfaks field, in the central part of the East Shetland basin in the northern North Sea, is operated by Statoil. The field was developed with three platforms and started production in Dec. 1986. Of more than 116 planned wells, 81 wells (including 6 subsea satellite wells) have been drilled. The field currently can produce about 600,000 BOPD, and estimated production life of the field is 20 years. The main drive mechanism is water injection. Predicted ultimate oil production from the field is 1,590 million bbl. About 465 million bbl was produced by Nov. 1993. Forecasted ultimate production represents 46% field recovery. Oil is produced from three major sandstone units: the Brent group, the Cook formation, and the Statfjord formation. The Etive/Rannoch formations of the Lower Brent group contain about 33% of mapped HCPV for the field. The reservoirs are overpressured, with an initial reservoir pressure of 4,495 psi at datum depth (6,070 ft below mean sea level) and 158°F. The shallow, highly porous sands are generally poorly consolidated. The oil is undersaturated, with a saturation pressure of about 3,550 psi, depending on formation depth and location.

Post-Frac Productivity Calculation for Complex Reservoir/Fracture Geometry

“…This gave a predicted PI of 16.5 bopd/psi (38 Sml/day/bar) .1. 2 One month after the frac job, post-frac PI was tested up to 16 bopd/psi (37 Sm1/daylbar), slowly building up to 19.5 bopd/psi (45 Sml/day/bar) at an associated rate of 12,500 bopd (2000 Sm)/day). This was in good agreement with predictions.…”

Frac and Pack Stimulation: Application, Design, and Field Experience From the Gulf of Mexico to Borneo

“…The pumping schedule and job results are listed in Tables 1 and 3. The Frac & Packed well had a much lower skin (12) than the equivalent IGP well (45) -though not as low as the corresponding EGP well (6). The F&P design value was lower (2), but was not achieved in practice -probably because fracture growth did not stop at TSO, which reduced the final fracture width.…”

“…In addition, F&P has great potential for completing wells in thin sand-shale laminated reservoirs: fracturing connects the individual reservoirs to the wellbore, allowing them to be depleted evenly. It has also been used for completing distant reservoirs by fracturing from a perforated interval that does not penetrate the target zone [6]. Furthermore, F&P can mitigate pressure-dependent processes leading to well inflow impairment such as deposition of asphaltenes, wax and sulphur.…”

Screenless Completions: Cost-Effective Sand Control in the Adriatic Sea

“…Bale et al 2 applied the indirect vertical fracturing technique to produce a weak formation sand free. In this method a stronger interval is perforated adjacent to the weak target interval and a hydraulic fracture is designed to grow into the target zone.…”