Experience Using Microbubbles-Aphron Drilling Fluid in Mature Reservoirs of Lake Maracaibo

Abstract

The objective of the paper is to present field results obtained through the evaluation of the Micro-bubble Aphron system, as the drilling fluid in wells VLA-1321, VLA-1325, VLA-1326, VLA-1327, VLA-1329, VLA-1331, VLA-1332, VLA-1334 and VLA-1335 (wells corresponding to Lagomar Integrated Laboratory). This fluid does not require equipment such as compressors, rotary wellhead, equipment to generate and/or inject nitrogen and permits the taking of electric logs conventionally. During drilling, mud weight varied between 6.8 to 7.9 ppg and very low-pressure zones were run through, with equivalent gradients oscillating between 2.4 ppg and 6.4 ppg, without any problems of loss of circulation. The micro-bubble fluid presented excellent inhibition values to clay and shale since the Miocene sands of Basal La Rosa and the alternating sand and shale of the Eocene reservoirs were drilled without any problems. Moreover, in well VLA-1321, this lithology was with an exposure time of 25 days, without any instability problem. On the other hand, in wells VLA-1329, VLA-1331, VLA-1332, VLA-1334 and VLA-1335 all the intervals were drilled from 1520' to 6900', without using intermediate casing and without great problems, which cut down drilling time to 31.0 days with a saving of 4.7 MMUS$ for the corporation. It should be pointed out that the fluid has presented rheological properties, which have permitted drilling with excellent hole cleaning. During the drilling of well VLA-1321, 90' of samples were taken in the Miocene and 300' in the Eocene sands with a high percentage of recovery (90.80%) and in well VLA-1326, 411' of samples were cut with a percentage of recovery of 90.4%. Additionally, the electric logs were not affected by the micro-buble mud and caliper logs showed a hole of excellent gage. Judging from the excellent results obtained, the Micro-bubble Aphron system is still being evaluated in the Eocene mature reservoirs of Lake Maracaibo. Introduction The Lagomar Integrated Laboratory (L.I.L.) comprises a first stage with the drilling of five vertical wells in order to increase the recovery up to 10% of the POES in the next five years, in the La Rosa Basal sands and "C" of the Eocene through the application of forefront technologies that permit high fluid volumes in the mature reservoirs and with low pressures. Due to the low gradients of the Eocene sands, the use of a drilling fluid which guarantees the integrity of the hole, without the risk of loss of circulation and with a minimum damage to the productive formation, is necessary. Recently, experiences have been had with aerated fluids, but the wells presented serious operational problems, such as: lost circulation, caving in of the holes due to the presence of unstable shale, impossibility of running logs, pressure taking, taking of samples, etc. A new system has been developed, a water base drilling fluid called Micro-bubble – Aphron, designed to drill low pressure mature reservoirs; this system is characterized as having in its continuous phase, high viscosity at low shear rate and containing, as internal phase, micro air or gas bubbles, non coalescing and recirculatable. These Micro-bubbles denominated "APHRONS" are generated by the use of a chemical surfactant that traps the air present in the system (active tank) and/or that is generated at pressure drop created by the jets of the bits. This fluid does not require an external source of injection of air and/or gas (compressors, equipment to generate and/or inject gas, etc.). The Aphrons permits reducing the density of the continuous phase to lesser values than water and the use of balance drilling technique.

Mathematical modeling of the Colloidal Gas Aphron transport through porous medium using the filtration theory

“…Recently, Aphron fluids have been successfully employed in drilling depleted reservoirs or formations which had previously experienced huge fluid losses (Brookey, 1998) (Ivan et al, 2001) (Ramirez et al, 2002) (Bjorndalen and Kuru, 2008). Brookey was the first one who introduced Aphrons for horizontal well drilling.…”

“…In this type of drilling operation, fluid pressure must be maintained at a higher level than the formation pressure, but the pressure difference must not be so high to avoid fluid invasion into the formation rock (Belkin et al, 2005). Although more experimental investigation is carried out on Aphron fluid filtration and its related parameters (Sebba, 1987) (Brookey, 1998) (Ivan et al, 2001) (Ramirez et al, 2002) (Bjorndalen and Kuru, 2008), a few modeling works were carried out in the literature (Belkin et al, 2005), recently Alizadeh and Khamehch have published some works on the Aphron modeling and flow through porous medium (Alizadeh and Khamehchi, 2015a) (Alizadeh and Khamehchi, 2015b) (Alizadeh and Khamehchi, 2016a) (Alizadeh and Khamehchi, 2016b) (Alizadeh and Khamehchi, 2016c) When a solid free fluid is created due to environmental issues, the use of Aphron drilling fluids is considered. Bridging in the front of the porous media in near wellbore zone, in fractured or depleted reservoirs, reduces the formation damage and fluid depth of invasion into the formation.…”

Experimental study of rheological properties of aphron based drilling Fluids and their effects on formation damage

“…Finally, the aphrons with cores formed of water-in-oil emulsion are called colloidal emulsion aphrons [5]. Todays, the use of CGA based uids is increasing in the petroleum industry because these uids exhibit properties that are desirable in operations in many elds [1,2,[6][7][8][9]. The potential of aphrons as components of drilling uids is due to their ability to form a solid, free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion through air microbubbles [10,11].…”

Herschel–Bulkley rheological parameters of lightweight colloidal gas aphron (CGA) based fluids

“…Finally, aphrons with cores formed of a waterin-oil emulsion are called colloidal emulsion aphrons (Deng et al, 2005). Currently, the use of CGA based fluids is increasing rapidly in the petroleum industry because these fluids exhibit properties that are desirable in many field operations (Brookey, 1998;Gregoire et al, 2005;Ivan et al, 2001;Ramirez et al, 2002;Rea et al, 2003;White et al, 2003). The potential of aphrons as components of drilling fluids rests in their ability to form a solid free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion by means of air microbubbles (Belkin et al, 2005;Growcock et al, 2003).…”