General information

Bore­hole drilling and sam­pling play a key role in var­i­ous indus­tries, from oil explo­ration to envi­ron­men­tal stud­ies. These process­es pro­vide valu­able infor­ma­tion about the Earth’s sub­sur­face, help to under­stand geo­log­i­cal struc­tures, and enable the assess­ment of envi­ron­men­tal con­di­tions. With the devel­op­ment of tech­nolo­gies and sci­en­tif­ic method­olo­gies, bore­hole drilling and sam­pling have become essen­tial tools for both sci­en­tif­ic research and indus­tri­al appli­ca­tions.

Bore­hole drilling is the process of cre­at­ing a cylin­dri­cal open­ing in the Earth’s crust using spe­cial­ized equip­ment and tech­niques. It is wide­ly used in min­ing, oil and gas explo­ration, geot­her­mal ener­gy, water sup­ply, and envi­ron­men­tal inves­ti­ga­tions.

A bore­hole is a min­ing exca­va­tion of cylin­dri­cal or stepped-cylin­dri­cal shape, char­ac­ter­ized by a sig­nif­i­cant depth rel­a­tive to its cross-sec­tion. It con­sists of sev­er­al ele­ments: the col­lar (the begin­ning of the bore­hole, which may be locat­ed at the sur­face or under­ground), the bot­tom (the end of the bore­hole, which advances dur­ing drilling), and the walls form­ing the lat­er­al sur­face of the exca­va­tion.

Bore­holes may have dif­fer­ent diam­e­ters: ini­tial, inter­me­di­ate, and final. Diam­e­ters can vary widely—from 26 to 1500 mm or more, and in the case of shaft drilling may reach 5–6 meters.

Classification of boreholes by purpose

Explo­ration (prospect­ing) bore­holes are drilled to search for and study min­er­al deposits. They are con­struct­ed in areas where the pres­ence of valu­able min­er­als is expect­ed based on geo­log­i­cal sur­veys, in order to col­lect rock sam­ples, cores, or flu­ids for analy­sis and eval­u­a­tion.

Engi­neer­ing-geo­log­i­cal bore­holes are drilled to inves­ti­gate the geot­ech­ni­cal prop­er­ties of soils and rocks at a spe­cif­ic site. They are com­mon­ly used in civ­il engi­neer­ing and con­struc­tion projects to assess sub­sur­face con­di­tions.

Hydro­ge­o­log­i­cal bore­holes are drilled to study and extract ground­wa­ter, deter­min­ing its avail­abil­i­ty, quan­ti­ty, and qual­i­ty char­ac­ter­is­tics.

Pro­duc­tion bore­holes are used for the extrac­tion of liq­uid (water, brines, oil) and gaseous (nat­ur­al gas, heli­um, etc.) min­er­al resources.

Dewa­ter­ing bore­holes are drilled to tem­porar­i­ly low­er the ground­wa­ter lev­el with­in a spe­cif­ic area and are wide­ly used in con­struc­tion and min­ing oper­a­tions.

Seis­mic bore­holes are drilled for geo­phys­i­cal (seis­mic) inves­ti­ga­tions using explo­sive ener­gy sources.

Drainage bore­holes are con­struct­ed to reduce excess water accu­mu­la­tion on irri­gat­ed land or to elim­i­nate haz­ardous flood­ing process­es.

Aux­il­iary and tech­ni­cal bore­holes, also referred to as ser­vice or sup­port bore­holes, are drilled for var­i­ous aux­il­iary or tech­ni­cal pur­pos­es relat­ed to spe­cif­ic projects or oper­a­tions.

Methods of borehole drilling

1) Mechan­i­cal rotary drilling:
Auger drilling – used for rel­a­tive­ly shal­low bore­holes and is one of the most com­mon meth­ods;
Core drilling – used to recov­er cylin­dri­cal core sam­ples and is capa­ble of pen­e­trat­ing all rock types.

2) Mechan­i­cal per­cus­sive drilling com­bines rotary and impact action by using a down­hole ham­mer dur­ing drilling.

3) Mechan­i­cal vibra­to­ry drilling (vibro-drilling) is based on the appli­ca­tion of high-fre­quen­cy vibra­tions trans­mit­ted to the drilling tool, reduc­ing fric­tion and increas­ing drilling effi­cien­cy.

4) Rotary drilling involves the use of a rotat­ing drill bit with cir­cu­la­tion of drilling flu­id to cool and lubri­cate the bit and to remove cut­tings to the sur­face.

5) Cable-tool drilling uses the ener­gy of falling weights to cre­ate an impact effect and is effec­tive in loose or uncon­sol­i­dat­ed soils.

Types of samples collected during borehole drilling

Cut­tings – small rock frag­ments car­ried to the sur­face by drilling flu­id, pro­vid­ing infor­ma­tion on lithol­o­gy and stratig­ra­phy.

Drilling flu­id sam­ples are ana­lyzed to assess drilling con­di­tions, for­ma­tion prop­er­ties, and the pos­si­ble pres­ence of for­ma­tion flu­ids.

Core sam­ples pro­vide detailed infor­ma­tion on the phys­i­cal, mechan­i­cal, and min­er­alog­i­cal prop­er­ties of rocks.

Flu­id sam­ples are used to ana­lyze the com­po­si­tion of water, brines, or for­ma­tion flu­ids encoun­tered dur­ing drilling.

Bore­hole wall sam­ples (side­wall cores) are tak­en to study for­ma­tion prop­er­ties in inter­vals where con­ven­tion­al cor­ing was not per­formed.

Com­pre­hen­sive analy­sis of the col­lect­ed sam­ples pro­vides a detailed under­stand­ing of sub­sur­face geol­o­gy, reser­voir poten­tial, and over­all bore­hole char­ac­ter­is­tics.

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