A universal fluid (UF) is typically a water-base fluid that has been treated with finely ground blast furnace slag and that still maintains the appropriate characteristics of a good drilling fluid. The slag becomes concentrated in the filter cake formed while drilling permeable formations and slowly sets to form a hard layer intimately bonded to the formation. True zonal isolation can be obtained by using a UF and subsequently cementing with slag-based mud solidification technology. Complete mud displacement and efforts to remove filter cake are not necessary prior to cementing since the solidified UF filter cake bonds strongly both to the formation and to the cement and since undisplaced portions of the UF set up as well. The universal fluid (UF) has been developed primarily out of the need to improve cementing in horizontal and extended-reach wells. To date UFs have been used to improve zonal isolation and to reduce or prevent lost circulation or cement fallback during drilling and cementing. Two Diatomite wells in the Belridge Field, California and the vertical portion of one horizontal well in the Midway Sunset Field, California were successfully drilled with a UF and cemented with slag mix cement slurries. Also, a well in the Midway Sunset Field, where losses are routinely experienced, was drilled with a UF specifically to control lost circulation, and no losses were experienced. Five wells in the Peace River area in Canada were successfully drilled with aUF to prevent cement fallback upon cementing.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Pirital Field is located in the eastern basin of Venezuela and is characterized by large high-pressure/high-temperature (HP/HT) reservoirs. The geology is complex with heavy faulting, natural fracturing and high-formation dip angles. To optimize the evaluation of the new HP/HT reservoirs in the Bosque block, a development and delineation project team was assembled. To fully assess the potential of the HP/HT reservoirs, two exploratory wells were drilled (PIC-25 and PIC-26) to confirm the feasibility of drilling and completing these wells. The mission of the project team was to deliver prolific producers with optimum completion efficiency while minimizing environmental impact.One of the most important tasks was the perforation planning to ensure adequate connectivity to the reservoir in order to successfully test and evaluate each respective horizon. Available petrophysical data indicated that the reservoirs under study were of low porosity (<5%) and permeability (<0.8 md) at a measured depth of 21,000 ft. Several perforating strategies were evaluated, and the final decision was to use propellant-assisted perforating in scenarios where conventional hydraulic fracturing was not in the evaluation plans.This paper covers the methodology used to validate the application of propellant-assisted perforating in HP/HT wells. The perforation-gun assembly selection, along with the analysis of generated peak pressures from the propellant burn process, will be reviewed. The mechanical configuration, wire line design and benefits derived from propellants will be fully explained.The results presented in the two case histories presented will show the benefits observed in the form of low completion skin factors. Propellant-assisted perforating has shown to be an effective method for achieving perforation breakdown when testing tight, HP/HT sandstone reservoirs. Perforating Techniques Pirital and North Monagas AreaTight sandstone formations are typically hydraulically fractured to obtain adequate flow rates required for production testing. Since the two PIC wells were considered to be tight, NomenclatureBHP = bottomhole pressure, psia (Kpa) BHT = bottomhole temperature, ºF (ºC) PI = initial reservoir pressure, psia (Kpa) Pwf = flowing bottomhole pressure, psia (Kpa) k = permeability, md kh = permeability thickness, md-ft C = wellbore storage constant, bbl/psi (m 3 /Kpa) S = skin factor, dimensionless Xf = fracture half-length, ft (m) PI = productivity index, bbl/day/psi (m 3 /day/Kpa)
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