Under­ground stor­age facil­i­ties are used to accu­mu­late strate­gic reserves of crude oil, petrol, diesel fuel, avi­a­tion kerosene and oth­er liq­uid hydro­car­bons. Com­pared with above-ground tanks, they are bet­ter pro­tect­ed against fires, acci­dents, sab­o­tage, mil­i­tary attacks and tem­per­a­ture fluc­tu­a­tions.

The devel­op­ment of such facil­i­ties requires a com­pre­hen­sive assess­ment of the geo­log­i­cal struc­ture, rock prop­er­ties, hydro­ge­o­log­i­cal con­di­tions, and poten­tial envi­ron­men­tal and tech­no­log­i­cal risks.

Main Types of Underground Storage Facilities

The type of under­ground stor­age facil­i­ty is select­ed accord­ing to the geo­log­i­cal struc­ture of the area, phys­i­cal and mechan­i­cal prop­er­ties of the rocks, hydro­ge­o­log­i­cal con­di­tions, type of petro­le­um prod­uct and required stor­age capac­i­ty.

• arti­fi­cial cav­erns cre­at­ed in rock salt deposits;
• under­ground cham­bers and tun­nels con­struct­ed in sta­ble rock for­ma­tions;
• cer­tain deplet­ed hydro­car­bon fields;
• con­vert­ed mine work­ings;
• oth­er nat­ur­al or arti­fi­cial­ly cre­at­ed under­ground cav­i­ties whose suit­abil­i­ty has been con­firmed by spe­cialised stud­ies.

Storage Facilities in Rock Salt Deposits

One of the most wide­ly used tech­nolo­gies involves the cre­ation of under­ground cav­i­ties in salt for­ma­tions by solu­tion min­ing. Water is inject­ed into a rock salt for­ma­tion through a well, dis­solv­ing the salt and grad­u­al­ly form­ing a cav­ern of the required shape and vol­ume.

Rock salt has very low per­me­abil­i­ty and is capa­ble of plas­tic defor­ma­tion. As a result, small frac­tures in the salt mass may close nat­u­ral­ly, help­ing to main­tain the integri­ty of the stor­age facil­i­ty.

• crude oil;
• diesel fuel;
• petrol and oth­er light petro­le­um prod­ucts;
• liq­ue­fied petro­le­um gas­es;
• oth­er types of strate­gic ener­gy resources.

Before a cav­ern is cre­at­ed, it is nec­es­sary to inves­ti­gate the depth, thick­ness and uni­for­mi­ty of the salt for­ma­tion, as well as the pres­ence of insol­u­ble inter­lay­ers, tec­ton­ic faults and aquifers.

Underground Chamber and Tunnel Storage

Under­ground cham­ber and tun­nel stor­age facil­i­ties are con­struct­ed in strong rock for­ma­tions, includ­ing gran­ite, gneiss, lime­stone and oth­er sta­ble geo­log­i­cal mass­es. The under­ground open­ings may be designed as cham­bers, gal­leries or tun­nels with addi­tion­al seal­ing sys­tems.

In some projects, con­tain­ment is pro­vid­ed by a hydraulic bar­ri­er. The stor­age facil­i­ty is con­struct­ed below the ground­wa­ter lev­el so that water pres­sure is direct­ed towards the under­ground open­ing and pre­vents petro­le­um prod­ucts from escap­ing into the sur­round­ing rock mass.

Such facil­i­ties may offer sub­stan­tial stor­age capac­i­ty, but they require com­plex min­ing oper­a­tions, ven­ti­la­tion and drainage sys­tems, fire pro­tec­tion, and con­tin­u­ous geot­ech­ni­cal mon­i­tor­ing.

Use of Depleted Hydrocarbon Fields

Cer­tain deplet­ed oil fields or oth­er suit­able reser­voir struc­tures may be con­sid­ered for crude oil stor­age. The suit­abil­i­ty of each facil­i­ty must be con­firmed through spe­cialised geo­log­i­cal, geo­phys­i­cal and hydro­dy­nam­ic inves­ti­ga­tions.

• remain­ing hydro­car­bon reserves;
• reser­voir poros­i­ty and per­me­abil­i­ty;
• integri­ty of the cap rock;
• con­di­tion of pre­vi­ous­ly drilled wells;
• pos­si­bil­i­ty of con­trolled prod­uct injec­tion and with­draw­al;
• risk of flu­id migra­tion between for­ma­tions;
• envi­ron­men­tal safe­ty and eco­nom­ic fea­si­bil­i­ty of the project.

Deplet­ed fields are more com­mon­ly used for under­ground nat­ur­al gas stor­age. Their use for crude oil and refined petro­le­um prod­ucts may require more com­plex tech­ni­cal solu­tions.

Conversion of Existing Mine Workings

Aban­doned mines, under­ground cham­bers and oth­er mine work­ings may poten­tial­ly be con­vert­ed into under­ground stor­age facil­i­ties. How­ev­er, the exis­tence of an under­ground cav­i­ty alone does not mean that it is suit­able for the safe stor­age of hydro­car­bons.

• sta­bil­i­ty of under­ground work­ings;
• frac­tur­ing and per­me­abil­i­ty of the sur­round­ing rocks;
• ground­wa­ter inflow path­ways;
• con­nec­tions with neigh­bour­ing mines and under­ground work­ings;
• con­di­tion of sup­port and seal­ing struc­tures;
• pres­ence of undoc­u­ment­ed mine work­ings and wells;
• pos­si­bil­i­ty of ensur­ing long-term con­tain­ment.

Advantages of Underground Storage

Under­ground stor­age can improve the pro­tec­tion of fuel infra­struc­ture while reduc­ing the sur­face area occu­pied by indus­tri­al facil­i­ties.

• pro­tec­tion against exter­nal mechan­i­cal impacts;
• low­er vul­ner­a­bil­i­ty to fires, sab­o­tage and mil­i­tary attacks;
• more sta­ble tem­per­a­ture con­di­tions;
• reduced loss of light frac­tions through evap­o­ra­tion;
• abil­i­ty to cre­ate sub­stan­tial strate­gic reserves;
• reduced use of sur­face land;
• low­er impact on the land­scape;
• poten­tial inte­gra­tion with pipelines, rail­way ter­mi­nals, ports and oil refiner­ies.

How­ev­er, under­ground place­ment does not elim­i­nate all risks. Such facil­i­ties require detailed geo­log­i­cal jus­ti­fi­ca­tion, integri­ty con­trol and con­tin­u­ous mon­i­tor­ing of the sur­round­ing rock mass.

Geological and Hydrogeological Requirements

The suit­abil­i­ty of a site for under­ground stor­age is deter­mined by a com­bi­na­tion of geo­log­i­cal, hydro­ge­o­log­i­cal, geo­me­chan­i­cal and envi­ron­men­tal fac­tors.

• litho­log­i­cal com­po­si­tion and phys­i­cal and mechan­i­cal prop­er­ties of the rocks;
• depth and thick­ness of the prospec­tive geo­log­i­cal for­ma­tion;
• frac­tur­ing and per­me­abil­i­ty of the rock mass;
• pres­ence of tec­ton­ic faults;
• cur­rent geo­dy­nam­ic activ­i­ty of the area;
• ground­wa­ter lev­els, flow regime and direc­tion;
• pro­tec­tion of drink­ing-water aquifers;
• rock sta­bil­i­ty dur­ing stor­age fill­ing and with­draw­al cycles;
• poten­tial impact on set­tle­ments, indus­tri­al facil­i­ties and pro­tect­ed areas.

The com­pat­i­bil­i­ty of oil or petro­le­um prod­ucts with the sur­round­ing rocks, for­ma­tion water, cement mate­ri­als, met­al struc­tures and insu­lat­ing coat­ings must also be inves­ti­gat­ed.

Stages of Underground Storage Development

The devel­op­ment of an under­ground stor­age facil­i­ty begins with the iden­ti­fi­ca­tion and geo­log­i­cal eval­u­a­tion of a suit­able site. The scope and sequence of work depend on the type of geo­log­i­cal for­ma­tion, planned stor­age capac­i­ty and prod­uct to be stored.

• col­lec­tion and analy­sis of avail­able geo­log­i­cal, geo­phys­i­cal and hydro­ge­o­log­i­cal infor­ma­tion;
• iden­ti­fi­ca­tion of prospec­tive geo­log­i­cal for­ma­tions;
• pre­lim­i­nary com­par­i­son of poten­tial sites;
• field geo­log­i­cal and geo­phys­i­cal sur­veys;
• drilling of explo­ration and engi­neer­ing-geo­log­i­cal wells;
• lab­o­ra­to­ry exam­i­na­tion of core sam­ples, rocks and ground­wa­ter;
• devel­op­ment of three-dimen­sion­al geo­log­i­cal and hydro­ge­o­log­i­cal mod­els;
• assess­ment of struc­tur­al sta­bil­i­ty and con­tain­ment integri­ty;
• assess­ment of envi­ron­men­tal and tech­no­log­i­cal risks;
• prepa­ra­tion of fea­si­bil­i­ty stud­ies and design doc­u­men­ta­tion;
• con­struc­tion and phased com­mis­sion­ing of the facil­i­ty;
• estab­lish­ment of a per­ma­nent mon­i­tor­ing sys­tem.

Monitoring and Safe Operation

The safe oper­a­tion of an under­ground stor­age facil­i­ty requires con­tin­u­ous mon­i­tor­ing of its tech­ni­cal con­di­tion and impact on the geo­log­i­cal envi­ron­ment.

• mon­i­tor­ing of pres­sure and tem­per­a­ture with­in the stor­age facil­i­ty;
• obser­va­tion of rock mass defor­ma­tion;
• inspec­tion of oper­at­ing and mon­i­tor­ing wells;
• mea­sure­ment of ground­wa­ter lev­els and pres­sure;
• mon­i­tor­ing of ground­wa­ter chem­istry;
• detec­tion of pos­si­ble oil or petro­le­um prod­uct leaks;
• inspec­tion of seal­ing and shut-off sys­tems;
• fore­cast­ing of changes in the geo­log­i­cal envi­ron­ment.

The mon­i­tor­ing pro­gramme is devel­oped indi­vid­u­al­ly and should remain in place through­out the entire oper­a­tional life of the facil­i­ty and, where nec­es­sary, after its clo­sure.

Potential for Underground Storage Development in Ukraine

Ukraine has a diverse geo­log­i­cal struc­ture that includes salt-bear­ing basins, thick sed­i­men­ta­ry sequences, crys­talline rock mass­es, mine work­ings and deplet­ed hydro­car­bon fields. This cre­ates favourable con­di­tions for iden­ti­fy­ing sites that may be suit­able for the under­ground stor­age of oil and petro­le­um prod­ucts.

How­ev­er, no geo­log­i­cal for­ma­tion can auto­mat­i­cal­ly be con­sid­ered suit­able for under­ground stor­age. Every poten­tial site requires sep­a­rate geo­log­i­cal, hydro­ge­o­log­i­cal, geo­me­chan­i­cal, envi­ron­men­tal and eco­nom­ic eval­u­a­tion.

The devel­op­ment of a net­work of under­ground stor­age facil­i­ties could improve the resilience of Ukraine’s fuel infra­struc­ture, pro­vide geo­graph­i­cal dis­tri­b­u­tion of reserves and reduce depen­dence on large above-ground oil depots.

Services Provided by the Institute of Geology

The Insti­tute of Geol­o­gy has the pro­fes­sion­al qual­i­fi­ca­tions required to per­form geo­log­i­cal, hydro­ge­o­log­i­cal, geo­phys­i­cal and engi­neer­ing-geo­log­i­cal work relat­ed to the iden­ti­fi­ca­tion, assess­ment and sub­stan­ti­a­tion of sites for the under­ground stor­age of oil and petro­le­um prod­ucts.

• iden­ti­fi­ca­tion of prospec­tive geo­log­i­cal for­ma­tions;
• selec­tion and com­par­a­tive assess­ment of poten­tial sites;
• analy­sis of geo­log­i­cal archives and exist­ing sur­vey mate­ri­als;
• organ­i­sa­tion of field sur­veys, drilling, geo­phys­i­cal inves­ti­ga­tions and lab­o­ra­to­ry test­ing;
• devel­op­ment of geo­log­i­cal and hydro­ge­o­log­i­cal mod­els;
• assess­ment of con­tain­ment integri­ty, struc­tur­al sta­bil­i­ty and tech­no­log­i­cal risks;
• prepa­ra­tion of geo­log­i­cal sub­stan­ti­a­tion and ini­tial data for project design;
• devel­op­ment of geo­log­i­cal and hydro­ge­o­log­i­cal mon­i­tor­ing pro­grammes.

The Insti­tute of Geol­o­gy is open to coop­er­a­tion with pub­lic author­i­ties, local com­mu­ni­ties, oil and gas com­pa­nies, investors and engi­neer­ing organ­i­sa­tions on the devel­op­ment of under­ground oil and petro­le­um prod­uct stor­age facil­i­ties in Ukraine’s geo­log­i­cal for­ma­tions.