Numerical simulations of the Macondo well blowout reveal strong control of oil flow by reservoir permeability and exsolution of gas

Abstract

In response to the urgent need for estimates of the oil and gas flow rate from the Macondo well MC252-1 blowout, we assembled a small team and carried out oil and gas flow simulations using the TOUGH2 codes over two weeks in mid-2010. The conceptual model included the oil reservoir and the well with a top boundary condition located at the bottom of the blowout preventer. We developed a fluid properties module (Eoil) applicable to a simple twophase and two-component oil-gas system. The flow of oil and gas was simulated using T2Well, a coupled reservoir-wellbore flow model, along with iTOUGH2 for sensitivity analysis and uncertainty quantification. The most likely oil flow rate estimated from simulations based on the data available in early June 2010 was about 100,000 bbl∕d (barrels per day) with a corresponding gas flow rate of 300 MMscf∕d (million standard cubic feet per day) assuming the well was open to the reservoir over 30 m of thickness. A Monte Carlo analysis of reservoir and fluid properties provided an uncertainty distribution with a long tail extending down to 60,000 bbl∕d of oil (170 MMscf∕d of gas). The flow rate was most strongly sensitive to reservoir permeability. Conceptual model uncertainty was also significant, particularly with regard to the length of the well that was open to the reservoir. For fluid-entry interval length of 1.5 m, the oil flow rate was about 56,000 bbl∕d. Sensitivity analyses showed that flow rate was not very sensitive to pressuredrop across the blowout preventer due to the interplay between gas exsolution and oil flow rate.Gulf oil spill | wellbore-reservoir coupling | phase interference O n April 20, 2010, the Macondo well MC252-1 drilled from the Deepwater Horizon floating platform in the Gulf of Mexico suffered a blowout. Eleven people were killed by the explosion and fire on the platform shortly after the blowout, and the platform sank 2 d later. The failure of the blowout preventer (BOP) mounted on the wellhead at the seafloor allowed oil and gas to flow directly into the sea out of the mangled riser pipe, which would normally convey oil from the well to the platform. Later the riser pipe was cut off, and oil and gas flowed directly into the sea out the top of the BOP. These details were displayed to the public in unprecedented fashion in real time over the internet by live video feeds from several remotely operated vehicles.

Porous Media Compressed-Air Energy Storage (PM-CAES): Theory and Simulation of the Coupled Wellbore–Reservoir System

“…We have developed T2Well, a numerical simulator for solving the equations of non-isothermal, multiphase, and multi-component flows in an integrated wellbore-reservoir system (e.g., Table 1), for a variety of applications (e.g., Pan et al 2011a, b;Oldenburg et al 2011), including PM-CAES. T2Well extends the existing numerical reservoir simulator TOUGH2 to calculate the flow in both the wellbore and the porous medium reservoir simultaneously and efficiently by introducing a special wellbore subdomain into the numerical grid.…”

Review of flow rate estimates of the Deepwater Horizon oil spill

“…They found effects of phase interference of gas and oil that were unanticipated such that oil flow rate is independent of the restriction in the BOP until P BOP equals about 6,600 psia (45 MPa), the pressure above which no gas exsolves (i.e., the Macondo hydrocarbons are single phase). Although a P BOP larger than 6,600 psia would imply that flow is restricted in the BOP, estimation of the precise degree of restriction for any assumed P BOP is complicated because of the strong interplay between pressure and gas exsolution in the whole system (reservoirwell-BOP) (15).…”

“…6), with the latter flow scenario resulting in significantly lower estimates of flow. One rather significant contribution from modeling was the capacity to consider the effect of restrictions in the BOP on flow rate (15). After the BOP was recovered from the seafloor, a postincident investigation was conducted to determine what could be concluded about the functioning of the various rams in the BOP system.…”

Low-Probability High-Consequence (LPHC) Failure Events in Geologic Carbon Sequestration Pipelines and Wells: Framework for LPHC Risk Assessment Incorporating Spatial Variability of Risk

“…The difficulty in killing the well likely arose from the complex geometry of flow paths in the well that prevented the pooling of kill fluid and promoted its atomization and transport up and out of the well entrained with natural gas. Similarly, the Macondo well in the Gulf of Mexico leaked oil and gas for approximately three months after the blowout preventer failed (Oldenburg et al, 2012). We recommend research aimed at modeling and simulation of well blowouts and kill processes in order to understand what kinds of well flow-path geometries are favorable and unfavorable for wellkilling.…”