Overbalanced drilling is the most common drilling technique; nevertheless, it has several disadvantages such as formation damage, mud losses, and stuck pipes; challenges that are common in high permeability zones and highly fractured formations. To overcome those issues, the underbalanced drilling method could be implemented. The underbalanced drilling (UBD) technique is widely utilized in hard, under pressure, depleted, and fractured/vuggy formations. Low-density drilling fluids are usually used in UBD operations and could be categorized into a gas (i.e., air, nitrogen, and natural gas) or two-phase (i.e., mist and foam). Although foamed fluid attracted attention in enhanced oil recovery and hydraulic fracturing operations, it is ideal for UBD operations due to its low density and efficient transport capacity. This paper highlights the applications, limitations, advantages, and disadvantages of UBD operations. It also discusses the drilling foam chemistry, structure, characterization, and rheological properties. Finally, this paper highlights a few successful UBD operations utilizing foamed drilling fluids worldwide.

Foamed acidic fluids have been utilized in the industry for enhanced oil recovery and fracturing applications due to their various advantages. Flowback enhancement, recovery of treatment fluids, and reduction of overall water consumption per operation are examples of these advantages. This study examines the utilization of a chelating agent, L-glutamic acid-N, N-diacetic acid (GLDA) in N2 and CO2 foamed fluids, which enhances the stability of foamed acidic fluids, lowers corrosion tendency, and is environmentally friendly. A modified high pressure and high temperature (HPHT) foam rheometer, and foam analyzer at ambient conditions, are used to test the acidic foamed fluids prepared in produced water using N2 and CO2. A screened out Alkyl diamine derivative surfactant has been tested at 212-300 °F and 1000 psi with and without GLDA. The effect of corrosion inhibitor addition on viscosity and foam quality is also investigated. Viscosity and foam quality measurements were done at increasing shear rates from 500 1/s up to 2000 1/s. Results showed that GLDA enhances the foamed fluid viscosity and stability. Resulted viscosities were in the range of 5 cP at higher shear rates to 25 cP in the lower shear rates region. Viscosity, in general, is lowered by higher shear rates, but foam quality is not affected. Fluid systems with a corrosion inhibitor also resulted in lower viscosities. The most stable and relatively higher viscosity values resulted from the 1 wt.% surfactant concentration with the addition of 15 wt.% GLDA and no corrosion inhibitor. Ambient conditions foam analyzer results showed higher foam height and half-life values of 182.8 mm and 16.5 minutes respectively when foaimg using N2 compared to 77.4 mm and 2.16 minutes when foamed with CO2. The addition of corrosion inhibitor showed significant negative impact in all cases, but least on the half-life of the CO2 foamed fluid. The rheology study provided did not consider the addition of thickeners which could be further investigated. This study covers the novel utilization of a chelating agent as an additive in CO2 and N2 acidic foamed fluids at harsh conditions. Furthermore, the fluid systems tested can be investigated and utilized as reliable stimulation fluid systems at temperatures up to 300 °F.

Summary This research fills the gap in understanding the impact of corrosion inhibitors (CIs) and a chelating agent on the rheology and stability of foam under harsh conditions. In this regard, a modified high-pressure, high-temperature (HPHT) foam rheometer and HPHT foam analyzer were used to investigate foam rheology and stability at 1,000 psi and 120 to 150°C with carbon dioxide (CO2) in the gas phase. Surfactant screening showed that Duomeen TTM and Armovis are thermally stable at high temperature and high water salinity and thus were used in this study. The liquid phase generally contained produced water (PW) (total dissolved solids ~ 24,611 ppm), 15 wt% chelating agent [L-glutamic acid-N, N-diacetic acid (GLDA)], and 1 wt% surfactant with and without a CI. First, we screened the viscosity and stability of Duomeen TTM and Armovis; the results showed that Duomeen TTM has a higher viscosity (at least by 82%) at a low shear rate, but both have similar viscosity at a higher shear rate. However, Armovis produced more stable foam. Once the GLDA was added to the Duomeen TTM solution, the viscosity increased significantly by 135% at a high shear rate (1,000–1,500). For the Armovis system, the viscosity improved by 77% and 68% at the low and high shear rates by adding GLDA. Additionally, foam stability was improved remarkably in both systems; half-life time almost doubled. Finally, we reported the effect of CI on the fluid systems, showing it considerably reduced the foam viscosity and stability. It reduced the half-life of the Armovis system by 79.4% and hindered the generation of foam for the Duomeen TTM system. A detailed discussion of foam properties, such as foamability, bubble count, and bubble radius, is provided. This study provides a wide-ranging understanding of additives’ impact on stimulating foam stability at HPHT.

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The injection of foam into petroleum reservoirs has attracted special interest in the last decades. Some applications include; fracturing, stimulation, and gas mobility control during gas EOR processes. Utilizing foam in well stimulation is promising as it consumes less water than water-based fracturing fluid, is less damaging to the formation, and provides an effective proppant carrying capacity and transportation. This paper studies the synergic effects of surfactant-polymer system on the rheology and stability of foamed acid at high temperature. A modified high-pressure, high-temperature (HPHT) foam rheometer was utilized to measure the apparent viscosity of CO2-foamed acid at 1,000 psi and 120 ℃. Additionally, a novel HPHT foam analyzer was used to characterize the following parameters; foamability, foam stability, foam structure, bubble count, and size under the same conditions. HPHT foam analyzer allows detecting the height and structure of foam all together as a function of the foam decay. Surfactant screening showed that Armovis is thermally stable at high temperatures and therefore was used in this work. Results showed that the polymer enhanced the foamed fluid viscosity significantly. The apparent foam viscosity increased by 43 %, once 0.5 wt% of superpusher polymer was synergic with 1 % Armovis-surfactant. The results of the HPHT foam analyzer indicated that the Armovis/polymer system is thermally stable and capable of resisting high salinity. The foam half-life improved by 12 times when 0.5 wt% of the polymer was added. Also, the bubble growth rate reduced remarkably, this improvement was due to the adsorption of surfactant and polymer molecules at the gas/liquid interface, which resulted in the reduction of gas permeability through the liquid film. This study investigates the synergy of polymer (superpusher SAV 522) and foamer (Armovis) in enhancing CO2 foam viscosity and stability at high pressure, temperature, and salinity. Furthermore, the surfactant-polymer systems evaluated can be investigated and used as stimulation fluid systems at temperatures up to 120 °C.