In accordance with one or more embodiments of the present disclosure, a method of subsurface sequestration of CO.sub.2 in a geological basin includes identifying one or more subsurface sequestration locations in the geological basin and injecting an aqueous CO.sub.2 solution to be sequestered into the geological basin. The one or more subsurface sequestration locations are regions of deeper geological structure, relative to an adjacent shallower geological structure, into which a negatively buoyant fluid injected into the basin will sink. The aqueous CO.sub.2 solution comprises a density that is greater than the density of the water naturally present in the geological basin, such that the injected aqueous CO.sub.2 solution pools in the one or more subsurface sequestration locations.

A multilateral well access system includes a directional guide and a mating surface profile. The directional guide includes a main body and an outer surface profile disposed on the main body. The main body defines a guide surface oriented non-parallelly to an elongate axis of the main body and a bore passing through the main body along the elongate axis. The mating surface profile is formed complementary to the outer surface profile of the directional guide and is engaged with the outer surface profile to secure the directional guide in a fixed position.

In accordance with one or more embodiments of the present disclosure, a method of subsurface sequestration of CO.sub.2 in a geological basin includes identifying one or more subsurface sequestration locations in the geological basin and injecting an aqueous CO.sub.2 solution to be sequestered into the geological basin. The one or more subsurface sequestration locations are regions of deeper geological structure, relative to an adjacent shallower geological structure, into which a negatively buoyant fluid injected into the basin will sink. The aqueous CO.sub.2 solution comprises a density that is greater than the density of the water naturally present in the geological basin, such that the injected aqueous CO.sub.2 solution pools in the one or more subsurface sequestration locations.

A method of drilling an uncompleted lateral wellbore in a subsurface formation includes drilling the uncompleted lateral wellbore with coiled tubing in the subsurface formation. The subsurface formation includes unconsolidated sand and the subsurface formation overlays a water-saturated reservoir. The method may further include introducing particles having an average particle size of from 8 mesh to 140 mesh into the uncompleted lateral wellbore, thereby supporting the uncompleted lateral wellbore and avoiding wellbore collapse and installing a screen in a vertical wellbore fluidly connected to the uncompleted lateral wellbore, wherein the screen has a mesh size of from 325 mesh to 1000 mesh. The subsurface formation may include hydrocarbons and the method may further include producing hydrocarbons from the subsurface formation.

Provided is a multilateral junction (MLT), a well system, and a method for forming a well system. The MLT, in one aspect, includes a y-block having a housing with a single first bore and second and third bores extending therein, the second and third bores defining second and third centerlines. The MLT, in this aspect, further includes a mainbore leg having a first mainbore leg end coupled to the second bore and a second opposing mainbore leg end, and a lateral bore leg having a first lateral bore leg end coupled to the third bore and a second opposing lateral bore leg end. In this aspect, the mainbore leg and the lateral bore leg are twisted with respect to the second and third bore such that a first plane taken through centerlines of the second opposing mainbore leg end and the second opposing lateral bore leg end is angled.

A multilateral junction comprising a y-block and a port seal member. The y-block comprises a main bore, a lateral bore, and lateral port formed in the y-block. The port seal member is integrated within the main bore and has at least one of an opened, closed, and choked position. The multilateral junction also includes one or more gaskets configured to hydraulically isolate the lateral bore when the port seal member is in a closed position. The multilateral junction may further include a controller coupled to the port seal member for performing at least one of an opening, closing, and choking operation on the port seal member. The y-block is a single, machined object with the main bore and the lateral bore formed therein. The multilateral junction is useful in applications that require pressure tight seals and minimal restriction of the internal diameter of a main bore.

Provided is a multilateral junction. The multilateral junction, in one aspect, includes a y-block. The multilateral junction additionally includes a mainbore leg coupled to the y-block, the mainbore leg defining a second overlapping space, and a lateral bore leg coupled to the y-block, the lateral bore leg defining a third overlapping space. The multilateral junction, in this aspect, additionally includes an expanded metal joint located in at least a portion of the second overlapping space or the third overlapping space, the expanded metal joint comprising a metal that has expanded in response to hydrolysis.

Provided is a downhole tool. The downhole tool, in one aspect, includes an isolation system for placement at a junction between a first wellbore and a secondary wellbore. In at least one aspect, the isolation system includes an elongated tubular, the elongated tubular having an opening connecting an interior of the elongated tubular and an exterior of the elongated tubular; and a slot located in the elongated tubular, the slot spanning the opening. In at least one aspect, the isolation system further includes an isolation sleeve located within the isolation system, the isolation sleeve configured to slide within the slot to either isolate the interior of the elongated tubular from the exterior of the elongated tubular or provide access between the interior of the elongated tubular and the exterior of the elongated tubular, and an I-shaped seal located in an annulus between the elongated tubular and the isolation sleeve.

Provided, in one aspect, are a downhole tool and a well system including a downhole tool. The downhole tool, in one aspect, includes a tubular, the tubular having an opening connecting an interior of the tubular and an exterior of the tubular. The downhole tool, in at least this aspect, includes first and second I-shaped seals on opposing sides of the opening, each of the first and second I-shaped seals including first and second opposing members, and a central member separating the first and second opposing members, the central member defining first and second fluid cavities.

Provided is a self-deflecting multilateral junction, a method, and a well system. The self-deflecting multilateral junction, in one aspect, includes a deflection device having an uphole end and a downhole end, the deflection device including a main tubular, a first flow path off the main tubular and operable to couple to a wellbore, a second flow path off the main tubular and operable to couple to a lateral wellbore, the second flow path having a lateral seal bore, and a deflecting ramp. The self-deflecting multilateral junction, according to this aspect, further includes a lateral stinger positioned within the main tubular and releasably coupled to the deflection device, the lateral stinger including a nose end configured to extend into the second flow path, a valve member, and a lateral seal for engaging the lateral seal bore.