Improving the Production Performance of Low-Permeability Natural Gas Hydrate Reservoirs by Radial Water Jet Slotting and Grouting in a Horizontal Well

Abstract

Most natural gas hydrate (NGH) reservoirs have poor permeability characteristics, which is unfavorable to fluid flow and gas production. To enhance gas production, a new method of radial water jet slotting and grouting (RWJSG) was proposed to reconstruct the formation around horizontal wellbores of a horizontal well. To evaluate the effectiveness of the proposed method, a three-dimensional (3D) gas production model was constructed with reference to the NGH reservoir at the SH2 site in the South China Sea (SCS). The results show that RWJSG can effectively enhance the gas recovery of the horizontal well. Compared with an unreconstructed case, the hydrate dissociation efficiency, cumulative gas production, and average ratio of gas to water production in the RWJSG case are increased by 121.0, 116.3 and 46.1%, respectively, during the 720day production period. RWJSG can enlarge reservoir exposed area, promote pressure drop transfer, and improve gas/water flow near the wellbore. In addition, the effect of increasing production mainly depends on the slot radius and number. Within a certain range, the decrease in slot spacing and increase in slot filler permeability have positive effects. For the reservoir at SH2 site, the scheme with a radius of 5 m, a spacing of 5 m, a number of 5 and a permeability of 500 mD could achieve remarkable stimulation effect. This work provides ideas and guidance for stimulation of horizontal wells in NGH reservoirs by RWJSG.

Enhancement of Gas Production from Class 1-Type Hydrate Reservoirs with High-Pressure Rotating Water Jets in Horizontal Well Depressurization Production

“…As indicated in Figure a, the reservoir was further separated into three sublayers: GHBL, TPL, and FGL, with thicknesses of 35, 15, and 27 m, respectively. , According to the model’s grid setting in the x – y plane, the minimum S (spacing) between stimulation zones can be set to 11.5 m, with a maximum Q (quantity) of stimulation zones of 25. Meanwhile, referring to stimulation parameter settings in similar research studies. , In this work, the W (width) of the stimulation zones is set to a fixed 0.5 m, while the maximum R (radius), K (permeability), and P (porosity) of the stimulation zones are set to 5.5 m, 5 D, and 0.7, respectively. To investigate the effects of different stimulation parameters on NGH production, we established seven groups of simulation scenarios, including 18 simulation cases (Figure b), and each horizontal well was deployed at the middle part of TPL ( Z = −62.5 m, from the top of the model), with an open-hole completion length of 300 m: (1) Group A: Cases 01 and 02 were designed to evaluate the yield increase performance of HPRWJ.…”

“…Figure depicts the schematic diagram of HPRWJ in marine sediments. After the horizontal well is drilled, the tool is lowered to the target location, and a high-pressure rotary water jet with sand or other mixtures is used to cut the sediment around the wellbore and form the disklike stimulation zone and the permeability can be up to 7.45 × 10 2 D. ,, According to previous studies, when the pumping pressure is 20 MPa, using the HPRWJ in the consolidated sediment can form a stimulation zone with a radius of 1 m and a width of 0.5 m, and the maximum pump pressure can reach 50 MPa . The shear strength of sediment containing hydrates is about 0.5 MPa, which is much lower than the shear strength of consolidated sediment (greater than 5 MPa).…”

“…Huang et al suggested using radial water jet slotting and grouting (RWJSG) technology to stimulate the near-well reservoir when extracting gas hydrate by horizontal well. The results showed that the RWJSG increased the cumulative gas production and the average gas-to-water ratio of the hydrate by 116.3 and 46.1%, respectively, during the 720-day production period …”

“…Previous research has substantially promoted the near-well stimulation technology in NGH production. However, previous work mainly focused on Class 3-type hydrate reservoirs, which are characterized by nonpermeable layers in both the upper and lower parts of the reservoir and a hydrate layer in the middle; the Class 1-type hydrate reservoir mainly consists of an upper hydrate layer and a lower free gas layer (FGL) (where gas and water can flow freely), and the performance of near-well stimulation technology in Class 1-type hydrate reservoirs is still unclear. − Thus, this work is a continuous investigation of hydrate extraction by horizontal well depressurization combined with HPRWJ technology in Class 1-type hydrate reservoirs. According to the research results of Wan et al, in the Class 1-type hydrate reservoir of the Shenhu Sea area, the horizontal wells deployed at the middle of the three-phase layer (TPL) can achieve the optimal gas-to-water ratio .…”