The　logging　results　from　the　Shenhu　Sea　show　that　the　P-T　conditions　of　NGH　deposits　are　below　the　CO2　hydrate　phase　equilibrium　curve.　The　burial　depth　difference　between　the　CO2　hydrate　stable　zone　and　NGH　deposits　is　usually　above　100　m,　which　differs　from　the　laboratory　scale.　Thus,　whether　CO2　hydrate　caps　can　provide　pore　sealing　and　reinforcement　of　natural　gas　hydrate　(NGH)　overburden　at　the　engineering　scale　is　unknown.　Based　on　this,　we　aimed　to　perfect　research　on　the　CO2　hydrate　cap,　including　its　formation　process,　effects　on　NGH　exploitation,　geomechanical　response,　and　comprehensive　benefit　evaluation,　by　establishing　a　THMC　model　based　on　Site　W17.　Results　indicate　that　(i)　CO2　can　form　hydrates　in　the　overburden　layer　with　a　conversion　rate　of　about　28%,　preventing　the　upward　escape　of　residual　liquid　CO2　due　to　density　difference.　(ii)　CO2　injection　and　CO2　hydrate　cap　formation　can　increase　the　decomposition　driving　force　during　depressurization　to　enhance　production,　but　it　fails　to　inhibit　water　invasion　from　the　upper　part　of　the　NGH　deposit　due　to　the　excessive　depth　difference.　(iii)　The　CO2　hydrate　cap　causes　strata　uplift,　thereby　mitigating　strata　subsidence　during　depressurization　production,　especially　for　the　cases　of　horizontal　wells,　where　the　subsidence　is　reduced　by　about　103.4%.　(iv)　Injecting　too　much　CO2　may　not　benefit　gas　production,　where　part　of　the　free　gas　will　convert　into　NGH　due　to　pressure　rise.　The　optimal　injection　rate　in　this　study　is　40,000　m3/d.　(v)　Indicators　like　CO2　hydrate　conversion　rate,　gas-water　ratio,　and　maximum　strata　displacement　show　that　horizontal　well　systems　with　CO2　hydrate　caps　are　more　beneficial　than　vertical　well　systems,　and　multi-branched　well　systems　are　more　beneficial　than　single-direction　well　systems.　These　key　findings　may　differ　from　the　laboratory　scale,　which　can　provide　a　reference　for　applying　CO2　hydrate　caps　in　actual　NGH　exploitation.　©　2024　Elsevier　Ltd